diff --git a/nixjs-rt/src/builtins.ts b/nixjs-rt/src/builtins.ts
index 7f01095..8e6d4a3 100644
--- a/nixjs-rt/src/builtins.ts
+++ b/nixjs-rt/src/builtins.ts
@@ -1,4 +1,4 @@
-import { err, errType, errTypes } from "./errors";
+import { err, errType, errTypes, highlighted } from "./errors";
 import { abortError } from "./errors/abort";
 import { otherError } from "./errors/other";
 import { typeMismatchError } from "./errors/typeError";
@@ -18,6 +18,7 @@ import {
   Path,
   TRUE,
 } from "./lib";
+import { dirOf, isAbsolutePath, normalizePath } from "./utils";
 
 type BuiltinsRecord = Record<string, (param: NixType) => NixType>;
 
@@ -341,7 +342,10 @@ export function getBuiltins() {
         );
       }
       if (listStrict.values.length === 0) {
-        throw otherError("Cannot fetch the first element in an empty list.");
+        throw otherError(
+          "Cannot fetch the first element in an empty list.",
+          "builtins-head-on-empty-list",
+        );
       }
       return listStrict.values[0];
     },
@@ -354,12 +358,26 @@ export function getBuiltins() {
         throw builtinBasicTypeMismatchError("import", pathStrict, expected);
       }
 
-      const pathValue = pathStrict.toJs();
+      let pathValue = "";
+      if (pathStrict instanceof NixString) {
+        pathValue = normalizePath(pathStrict.toJs());
+      } else if (pathStrict instanceof Path) {
+        pathValue = pathStrict.toJs();
+      }
+
+      // Check if it's an absolute path. Relative paths are not allowed.
+      // Path data types are always automatically absolute.
+      if (!isAbsolutePath(pathValue)) {
+        throw otherError(
+          err`string ${highlighted(JSON.stringify(pathValue))} doesn't represent an absolute path. Only absolute paths are allowed for imports.`,
+          "builtins-import-non-absolute-path",
+        );
+      }
 
-      const resultingFn: (ctx: EvalCtx) => NixType = importNixModule(pathValue);
+      const resultingFn = importNixModule(pathValue);
 
-      const ctx = new EvalCtx(pathValue);
-      return resultingFn(ctx);
+      const newCtx = new EvalCtx(dirOf(pathValue));
+      return resultingFn(newCtx);
     },
 
     intersectAttrs: (arg) => {
diff --git a/nixjs-rt/src/errors/other.ts b/nixjs-rt/src/errors/other.ts
index 8691a31..b00e1df 100644
--- a/nixjs-rt/src/errors/other.ts
+++ b/nixjs-rt/src/errors/other.ts
@@ -2,14 +2,21 @@ import { ErrorMessage, err, NixError, instanceToClass } from ".";
 import { NixTypeClass, NixTypeInstance } from "../lib";
 
 export class NixOtherError {
-  constructor(public readonly message: string) {}
+  constructor(
+    public readonly message: ErrorMessage,
+    public readonly codename: string,
+  ) {}
 
   toDefaultErrorMessage(): ErrorMessage {
-    return err`${this.message}`;
+    return this.message;
   }
 }
 
-export function otherError(message: string) {
-  let other = new NixOtherError(message);
+export function otherError(message: string | ErrorMessage, codename: string) {
+  if (typeof message === "string") {
+    message = err`${message}`;
+  }
+
+  let other = new NixOtherError(message, codename);
   return new NixError(other, other.toDefaultErrorMessage());
 }
diff --git a/nixjs-rt/src/lib.ts b/nixjs-rt/src/lib.ts
index 6e746cc..1184e7d 100644
--- a/nixjs-rt/src/lib.ts
+++ b/nixjs-rt/src/lib.ts
@@ -20,6 +20,7 @@ import {
   couldntFindVariableError,
 } from "./errors/variable";
 import { NixAbortError } from "./errors/abort";
+import { isAbsolutePath, joinPaths, normalizePath } from "./utils";
 
 // Error re-exports
 export { NixError } from "./errors";
@@ -535,6 +536,7 @@ class AttrsetBuilder implements Scope {
       if (attrPath.length === 0) {
         throw otherError(
           "Cannot add an undefined attribute name to the attrset.",
+          "attrset-add-undefined-attrname",
         );
       }
       const attrName = attrPath[0].toStrict();
@@ -1291,34 +1293,6 @@ export function recursiveStrictAttrset(theAttrset: Attrset): Attrset {
   return theAttrset;
 }
 
-function isAbsolutePath(path: string): boolean {
-  return path.startsWith("/");
-}
-
-function joinPaths(abs_base: string, path: string): string {
-  return `${abs_base}/${path}`;
-}
-
-function normalizePath(path: string): string {
-  let segments = path.split("/");
-  let normalizedSegments = new Array();
-  for (const segment of segments) {
-    switch (segment) {
-      case "":
-        break;
-      case ".":
-        break;
-      case "..":
-        normalizedSegments.pop();
-        break;
-      default:
-        normalizedSegments.push(segment);
-        break;
-    }
-  }
-  return (isAbsolutePath(path) ? "/" : "") + normalizedSegments.join("/");
-}
-
 /**
  * If given an attrset entry like `a = value`, then this function returns just the given value.
  * If the attrset has multiple segments (e.g. `a.b.c = value`), then this function returns
@@ -1330,7 +1304,10 @@ function _attrPathToValue(
   value: NixType,
 ): undefined | NixType {
   if (attrPath.length === 0) {
-    throw otherError("Unexpected attr path of zero length.");
+    throw otherError(
+      "Unexpected attr path of zero length.",
+      "attrset-attrpath-zero-length",
+    );
   }
 
   let attrName = attrPath[0].toStrict();
diff --git a/nixjs-rt/src/utils.ts b/nixjs-rt/src/utils.ts
new file mode 100644
index 0000000..6396920
--- /dev/null
+++ b/nixjs-rt/src/utils.ts
@@ -0,0 +1,33 @@
+export function isAbsolutePath(path: string): boolean {
+  return path.startsWith("/");
+}
+
+export function joinPaths(abs_base: string, path: string): string {
+  return `${abs_base}/${path}`;
+}
+
+export function normalizePath(path: string): string {
+  let segments = path.split("/");
+  let normalizedSegments: string[] = [];
+  for (const segment of segments) {
+    switch (segment) {
+      case "":
+        break;
+      case ".":
+        break;
+      case "..":
+        normalizedSegments.pop();
+        break;
+      default:
+        normalizedSegments.push(segment);
+        break;
+    }
+  }
+  return (isAbsolutePath(path) ? "/" : "") + normalizedSegments.join("/");
+}
+
+export function dirOf(path: string) {
+  // Return everything before the final slash
+  const lastSlash = path.lastIndexOf("/");
+  return path.substring(0, lastSlash);
+}
diff --git a/src/eval/error.rs b/src/eval/error.rs
index dfda09b..dc034b1 100644
--- a/src/eval/error.rs
+++ b/src/eval/error.rs
@@ -72,7 +72,7 @@ pub enum NixErrorKind {
         got: NixTypeKind,
     },
     Other {
-        message: String,
+        codename: String,
     },
     MissingAttribute {
         attr_path: Vec<String>,
@@ -153,9 +153,10 @@ fn try_js_error_to_rust(
             NixErrorKind::TypeMismatch { expected, got }
         }
         "NixOtherError" => {
-            let message_js = get_js_value_key(scope, &kind_js, "message")?;
-            let message = message_js.to_rust_string_lossy(scope);
-            NixErrorKind::Other { message }
+            let codename_js = get_js_value_key(scope, &kind_js, "codename")?;
+            let codename = codename_js.to_rust_string_lossy(scope);
+
+            NixErrorKind::Other { codename }
         }
         "NixMissingAttributeError" => {
             let attr_path_js = get_js_value_key(scope, &kind_js, "attrPath")?;
@@ -211,7 +212,7 @@ fn nix_type_class_to_enum(
                 "Unexpected type name: {name}"
             ))],
             kind: NixErrorKind::Other {
-                message: format!("Unexpected type name: {name}"),
+                codename: "unknown-type".to_owned(),
             },
         }),
     }
diff --git a/src/tests/builtins.rs b/src/tests/builtins.rs
index f9240bb..fe0a8f8 100644
--- a/src/tests/builtins.rs
+++ b/src/tests/builtins.rs
@@ -476,7 +476,7 @@ mod head {
         assert_eq!(
             eval_err("builtins.head []"),
             NixErrorKind::Other {
-                message: "Cannot fetch the first element in an empty list.".to_string()
+                codename: "builtins-head-on-empty-list".to_string()
             }
         );
     }