diff --git a/src/node_api.cc b/src/node_api.cc
index 8f8c400cdfbb21..fbf20878abd702 100644
--- a/src/node_api.cc
+++ b/src/node_api.cc
@@ -117,16 +117,23 @@ struct napi_env__ {
   CHECK_TO_TYPE((env), Boolean, (context), (result), (src), \
     napi_boolean_expected)
 
+// n-api defines NAPI_AUTO_LENGHTH as the indicator that a string
+// is null terminated. For V8 the equivalent is -1. The assert
+// validates that our cast of NAPI_AUTO_LENGTH results in -1 as
+// needed by V8.
 #define CHECK_NEW_FROM_UTF8_LEN(env, result, str, len)                   \
   do {                                                                   \
+    static_assert(static_cast<int>(NAPI_AUTO_LENGTH) == -1,              \
+                  "Casting NAPI_AUTO_LENGTH to int must result in -1");  \
     auto str_maybe = v8::String::NewFromUtf8(                            \
-        (env)->isolate, (str), v8::NewStringType::kInternalized, (len)); \
+        (env)->isolate, (str), v8::NewStringType::kInternalized,         \
+        static_cast<int>(len));                                          \
     CHECK_MAYBE_EMPTY((env), str_maybe, napi_generic_failure);           \
     (result) = str_maybe.ToLocalChecked();                               \
   } while (0)
 
 #define CHECK_NEW_FROM_UTF8(env, result, str) \
-  CHECK_NEW_FROM_UTF8_LEN((env), (result), (str), -1)
+  CHECK_NEW_FROM_UTF8_LEN((env), (result), (str), NAPI_AUTO_LENGTH)
 
 #define GET_RETURN_STATUS(env)      \
   (!try_catch.HasCaught() ? napi_ok \
@@ -918,21 +925,26 @@ NAPI_NO_RETURN void napi_fatal_error(const char* location,
                                      size_t location_len,
                                      const char* message,
                                      size_t message_len) {
-  char* location_string = const_cast<char*>(location);
-  char* message_string = const_cast<char*>(message);
-  if (location_len != -1) {
-    location_string = reinterpret_cast<char*>(
-        malloc(location_len * sizeof(char) + 1));
-    strncpy(location_string, location, location_len);
-    location_string[location_len] = '\0';
+  std::string location_string;
+  std::string message_string;
+
+  if (location_len != NAPI_AUTO_LENGTH) {
+    location_string.assign(
+        const_cast<char*>(location), location_len);
+  } else {
+    location_string.assign(
+        const_cast<char*>(location), strlen(location));
   }
-  if (message_len != -1) {
-    message_string = reinterpret_cast<char*>(
-        malloc(message_len * sizeof(char) + 1));
-    strncpy(message_string, message, message_len);
-    message_string[message_len] = '\0';
+
+  if (message_len != NAPI_AUTO_LENGTH) {
+    message_string.assign(
+        const_cast<char*>(message), message_len);
+  } else {
+    message_string.assign(
+        const_cast<char*>(message), strlen(message));
   }
-  node::FatalError(location_string, message_string);
+
+  node::FatalError(location_string.c_str(), message_string.c_str());
 }
 
 napi_status napi_create_function(napi_env env,
@@ -3285,7 +3297,6 @@ napi_status napi_adjust_external_memory(napi_env env,
                                         int64_t change_in_bytes,
                                         int64_t* adjusted_value) {
   CHECK_ENV(env);
-  CHECK_ARG(env, &change_in_bytes);
   CHECK_ARG(env, adjusted_value);
 
   *adjusted_value = env->isolate->AdjustAmountOfExternalAllocatedMemory(
diff --git a/src/node_api.h b/src/node_api.h
index 82f2e1900e2fe4..a3a07a64673366 100644
--- a/src/node_api.h
+++ b/src/node_api.h
@@ -100,6 +100,8 @@ typedef struct {
 #define NAPI_MODULE(modname, regfunc) \
   NAPI_MODULE_X(modname, regfunc, NULL, 0)
 
+#define NAPI_AUTO_LENGTH SIZE_MAX
+
 EXTERN_C_START
 
 NAPI_EXTERN void napi_module_register(napi_module* mod);
diff --git a/test/addons-napi/test_async/test_async.cc b/test/addons-napi/test_async/test_async.cc
index 251573828b9fe8..4d3e025097ba18 100644
--- a/test/addons-napi/test_async/test_async.cc
+++ b/test/addons-napi/test_async/test_async.cc
@@ -95,8 +95,8 @@ napi_value Test(napi_env env, napi_callback_info info) {
   NAPI_CALL(env,
     napi_create_reference(env, argv[2], 1, &the_carrier._callback));
 
-  NAPI_CALL(env,
-    napi_create_string_utf8(env, "TestResource", -1, &resource_name));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "TestResource", NAPI_AUTO_LENGTH, &resource_name));
   NAPI_CALL(env, napi_create_async_work(env, argv[1], resource_name,
     Execute, Complete, &the_carrier, &the_carrier._request));
   NAPI_CALL(env,
@@ -145,8 +145,8 @@ napi_value TestCancel(napi_env env, napi_callback_info info) {
   napi_value resource_name;
   void* data;
 
-  NAPI_CALL(env,
-    napi_create_string_utf8(env, "TestResource", -1, &resource_name));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "TestResource", NAPI_AUTO_LENGTH, &resource_name));
 
   // make sure the work we are going to cancel will not be
   // able to start by using all the threads in the pool
diff --git a/test/addons-napi/test_constructor/test_constructor.c b/test/addons-napi/test_constructor/test_constructor.c
index d742f2bcd1707b..70f53ec5a92f55 100644
--- a/test/addons-napi/test_constructor/test_constructor.c
+++ b/test/addons-napi/test_constructor/test_constructor.c
@@ -77,7 +77,7 @@ napi_value Init(napi_env env, napi_value exports) {
   };
 
   napi_value cons;
-  NAPI_CALL(env, napi_define_class(env, "MyObject", -1, New,
+  NAPI_CALL(env, napi_define_class(env, "MyObject", NAPI_AUTO_LENGTH, New,
       NULL, sizeof(properties)/sizeof(*properties), properties, &cons));
 
   NAPI_CALL(env, napi_create_reference(env, cons, 1, &constructor_));
diff --git a/test/addons-napi/test_conversions/test_conversions.c b/test/addons-napi/test_conversions/test_conversions.c
index eafe375d66eba7..4f92bafa35b79d 100644
--- a/test/addons-napi/test_conversions/test_conversions.c
+++ b/test/addons-napi/test_conversions/test_conversions.c
@@ -81,7 +81,8 @@ napi_value AsString(napi_env env, napi_callback_info info) {
     napi_get_value_string_utf8(env, args[0], value, sizeof(value), NULL));
 
   napi_value output;
-  NAPI_CALL(env, napi_create_string_utf8(env, value, -1, &output));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, value, NAPI_AUTO_LENGTH, &output));
 
   return output;
 }
diff --git a/test/addons-napi/test_env_sharing/compare_env.c b/test/addons-napi/test_env_sharing/compare_env.c
index da984b68f53f3e..6a93ce52c64025 100644
--- a/test/addons-napi/test_env_sharing/compare_env.c
+++ b/test/addons-napi/test_env_sharing/compare_env.c
@@ -15,7 +15,8 @@ napi_value compare(napi_env env, napi_callback_info info) {
 }
 
 napi_value Init(napi_env env, napi_value exports) {
-  NAPI_CALL(env, napi_create_function(env, "exports", -1, compare, NULL, &exports));
+  NAPI_CALL(env, napi_create_function(
+      env, "exports", NAPI_AUTO_LENGTH, compare, NULL, &exports));
   return exports;
 }
 
diff --git a/test/addons-napi/test_error/test_error.cc b/test/addons-napi/test_error/test_error.cc
index bd6cf8c2fe4800..4ab20bd7522a3b 100644
--- a/test/addons-napi/test_error/test_error.cc
+++ b/test/addons-napi/test_error/test_error.cc
@@ -18,7 +18,8 @@ napi_value checkError(napi_env env, napi_callback_info info) {
 napi_value throwExistingError(napi_env env, napi_callback_info info) {
   napi_value message;
   napi_value error;
-  NAPI_CALL(env, napi_create_string_utf8(env, "existing error", -1, &message));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "existing error", NAPI_AUTO_LENGTH, &message));
   NAPI_CALL(env, napi_create_error(env, nullptr,  message, &error));
   NAPI_CALL(env, napi_throw(env, error));
   return nullptr;
@@ -62,7 +63,8 @@ napi_value throwTypeErrorCode(napi_env env, napi_callback_info info) {
 napi_value createError(napi_env env, napi_callback_info info) {
   napi_value result;
   napi_value message;
-  NAPI_CALL(env, napi_create_string_utf8(env, "error", -1, &message));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "error", NAPI_AUTO_LENGTH, &message));
   NAPI_CALL(env, napi_create_error(env, nullptr, message, &result));
   return result;
 }
@@ -70,7 +72,8 @@ napi_value createError(napi_env env, napi_callback_info info) {
 napi_value createRangeError(napi_env env, napi_callback_info info) {
   napi_value result;
   napi_value message;
-  NAPI_CALL(env, napi_create_string_utf8(env, "range error", -1, &message));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "range error", NAPI_AUTO_LENGTH, &message));
   NAPI_CALL(env, napi_create_range_error(env, nullptr, message, &result));
   return result;
 }
@@ -78,7 +81,8 @@ napi_value createRangeError(napi_env env, napi_callback_info info) {
 napi_value createTypeError(napi_env env, napi_callback_info info) {
   napi_value result;
   napi_value message;
-  NAPI_CALL(env, napi_create_string_utf8(env, "type error", -1, &message));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "type error", NAPI_AUTO_LENGTH, &message));
   NAPI_CALL(env, napi_create_type_error(env, nullptr, message, &result));
   return result;
 }
@@ -87,8 +91,10 @@ napi_value createErrorCode(napi_env env, napi_callback_info info) {
   napi_value result;
   napi_value message;
   napi_value code;
-  NAPI_CALL(env, napi_create_string_utf8(env, "Error [error]", -1, &message));
-  NAPI_CALL(env, napi_create_string_utf8(env, "ERR_TEST_CODE", -1, &code));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "Error [error]", NAPI_AUTO_LENGTH, &message));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "ERR_TEST_CODE", NAPI_AUTO_LENGTH, &code));
   NAPI_CALL(env, napi_create_error(env, code, message, &result));
   return result;
 }
@@ -99,9 +105,10 @@ napi_value createRangeErrorCode(napi_env env, napi_callback_info info) {
   napi_value code;
   NAPI_CALL(env, napi_create_string_utf8(env,
                                          "RangeError [range error]",
-                                         -1,
+                                         NAPI_AUTO_LENGTH,
                                          &message));
-  NAPI_CALL(env, napi_create_string_utf8(env, "ERR_TEST_CODE", -1, &code));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "ERR_TEST_CODE", NAPI_AUTO_LENGTH, &code));
   NAPI_CALL(env, napi_create_range_error(env, code, message, &result));
   return result;
 }
@@ -112,9 +119,10 @@ napi_value createTypeErrorCode(napi_env env, napi_callback_info info) {
   napi_value code;
   NAPI_CALL(env, napi_create_string_utf8(env,
                                          "TypeError [type error]",
-                                         -1,
+                                         NAPI_AUTO_LENGTH,
                                          &message));
-  NAPI_CALL(env, napi_create_string_utf8(env, "ERR_TEST_CODE", -1, &code));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "ERR_TEST_CODE", NAPI_AUTO_LENGTH, &code));
   NAPI_CALL(env, napi_create_type_error(env, code, message, &result));
   return result;
 }
diff --git a/test/addons-napi/test_fatal/test_fatal.c b/test/addons-napi/test_fatal/test_fatal.c
index 6d8fa6ff8613f2..add8bebf3be7e3 100644
--- a/test/addons-napi/test_fatal/test_fatal.c
+++ b/test/addons-napi/test_fatal/test_fatal.c
@@ -2,7 +2,8 @@
 #include "../common.h"
 
 napi_value Test(napi_env env, napi_callback_info info) {
-  napi_fatal_error("test_fatal::Test", -1, "fatal message", -1);
+  napi_fatal_error("test_fatal::Test", NAPI_AUTO_LENGTH,
+                   "fatal message", NAPI_AUTO_LENGTH);
   return NULL;
 }
 
diff --git a/test/addons-napi/test_function/test_function.c b/test/addons-napi/test_function/test_function.c
index 5ce06d670609c1..b0350e6ee22876 100644
--- a/test/addons-napi/test_function/test_function.c
+++ b/test/addons-napi/test_function/test_function.c
@@ -33,11 +33,11 @@ napi_value TestFunctionName(napi_env env, napi_callback_info info) {
 napi_value Init(napi_env env, napi_value exports) {
   napi_value fn1;
   NAPI_CALL(env, napi_create_function(
-      env, NULL, -1, TestCallFunction, NULL, &fn1));
+      env, NULL, NAPI_AUTO_LENGTH, TestCallFunction, NULL, &fn1));
 
   napi_value fn2;
   NAPI_CALL(env, napi_create_function(
-      env, "Name", -1, TestFunctionName, NULL, &fn2));
+      env, "Name", NAPI_AUTO_LENGTH, TestFunctionName, NULL, &fn2));
 
   napi_value fn3;
   NAPI_CALL(env, napi_create_function(
diff --git a/test/addons-napi/test_general/test_general.c b/test/addons-napi/test_general/test_general.c
index 099c1315c071fe..05cdd76e3c1e64 100644
--- a/test/addons-napi/test_general/test_general.c
+++ b/test/addons-napi/test_general/test_general.c
@@ -43,7 +43,7 @@ napi_value testGetNodeVersion(napi_env env, napi_callback_info info) {
   NAPI_CALL(env, napi_create_uint32(env, node_version->patch, &patch));
   NAPI_CALL(env, napi_create_string_utf8(env,
                                          node_version->release,
-                                         (size_t)-1,
+                                         NAPI_AUTO_LENGTH,
                                          &release));
   NAPI_CALL(env, napi_create_array_with_length(env, 4, &result));
   NAPI_CALL(env, napi_set_element(env, result, 0, major));
@@ -120,21 +120,29 @@ napi_value testNapiTypeof(napi_env env, napi_callback_info info) {
 
   napi_value result = NULL;
   if (argument_type == napi_number) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "number", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "number", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_string) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "string", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "string", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_function) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "function", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "function", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_object) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "object", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "object", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_boolean) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "boolean", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "boolean", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_undefined) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "undefined", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "undefined", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_symbol) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "symbol", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "symbol", NAPI_AUTO_LENGTH, &result));
   } else if (argument_type == napi_null) {
-    NAPI_CALL(env, napi_create_string_utf8(env, "null", -1, &result));
+    NAPI_CALL(env, napi_create_string_utf8(
+        env, "null", NAPI_AUTO_LENGTH, &result));
   }
   return result;
 }
diff --git a/test/addons-napi/test_make_callback/binding.cc b/test/addons-napi/test_make_callback/binding.cc
index 8a6d94985c1962..4b0537ca07cf17 100644
--- a/test/addons-napi/test_make_callback/binding.cc
+++ b/test/addons-napi/test_make_callback/binding.cc
@@ -25,7 +25,8 @@ napi_value MakeCallback(napi_env env, napi_callback_info info) {
   NAPI_CALL(env, napi_typeof(env, func, &func_type));
 
   napi_value resource_name;
-  NAPI_CALL(env, napi_create_string_utf8(env, "test", -1, &resource_name));
+  NAPI_CALL(env, napi_create_string_utf8(
+      env, "test", NAPI_AUTO_LENGTH, &resource_name));
 
   napi_async_context context;
   NAPI_CALL(env, napi_async_init(env, func, resource_name, &context));
@@ -45,7 +46,8 @@ napi_value MakeCallback(napi_env env, napi_callback_info info) {
 
 napi_value Init(napi_env env, napi_value exports) {
   napi_value fn;
-  NAPI_CALL(env, napi_create_function(env, NULL, -1, MakeCallback, NULL, &fn));
+  NAPI_CALL(env, napi_create_function(
+      env, NULL, NAPI_AUTO_LENGTH, MakeCallback, NULL, &fn));
   NAPI_CALL(env, napi_set_named_property(env, exports, "makeCallback", fn));
   return exports;
 }
diff --git a/test/addons-napi/test_make_callback_recurse/binding.cc b/test/addons-napi/test_make_callback_recurse/binding.cc
index 212c9ec4022fa3..714e44773de623 100644
--- a/test/addons-napi/test_make_callback_recurse/binding.cc
+++ b/test/addons-napi/test_make_callback_recurse/binding.cc
@@ -20,7 +20,8 @@ napi_value MakeCallback(napi_env env, napi_callback_info info) {
 
 napi_value Init(napi_env env, napi_value exports) {
   napi_value fn;
-  NAPI_CALL(env, napi_create_function(env, NULL, -1, MakeCallback, NULL, &fn));
+  NAPI_CALL(env, napi_create_function(
+      env, NULL, NAPI_AUTO_LENGTH, MakeCallback, NULL, &fn));
   NAPI_CALL(env, napi_set_named_property(env, exports, "makeCallback", fn));
   return exports;
 }
diff --git a/test/addons-napi/test_properties/test_properties.c b/test/addons-napi/test_properties/test_properties.c
index 4c3394e0e0349e..a95c7013c2cabb 100644
--- a/test/addons-napi/test_properties/test_properties.c
+++ b/test/addons-napi/test_properties/test_properties.c
@@ -66,14 +66,14 @@ napi_value Init(napi_env env, napi_value exports) {
   napi_value name_value;
   NAPI_CALL(env, napi_create_string_utf8(env,
                                          "NameKeyValue",
-                                         -1,
+                                         NAPI_AUTO_LENGTH,
                                          &name_value));
 
   napi_value symbol_description;
   napi_value name_symbol;
   NAPI_CALL(env, napi_create_string_utf8(env,
                                          "NameKeySymbol",
-                                         -1,
+                                         NAPI_AUTO_LENGTH,
                                          &symbol_description));
   NAPI_CALL(env, napi_create_symbol(env,
                                     symbol_description,