diff --git a/src/bmffimage.cpp b/src/bmffimage.cpp
index 85fd21f051..b8d2245d67 100644
--- a/src/bmffimage.cpp
+++ b/src/bmffimage.cpp
@@ -93,7 +93,7 @@ std::string BmffImage::toAscii(uint32_t n) {
   // show 0 as _
   std::replace(result.begin(), result.end(), '\0', '_');
   // show non 7-bit printable ascii as .
-  auto f = [](unsigned char c) { return !std::isprint(c); };
+  auto f = [](char c) { return c < 32 || c > 126; };
   std::replace_if(result.begin(), result.end(), f, '.');
   return result;
 }
diff --git a/src/image_int.hpp b/src/image_int.hpp
index b195ebd053..1f9b6f5243 100644
--- a/src/image_int.hpp
+++ b/src/image_int.hpp
@@ -50,8 +50,9 @@ template <typename T>
 std::ostream& operator<<(std::ostream& stream, const binaryToStringHelper<T>& binToStr) {
   for (size_t i = 0; i < binToStr.buf_.size(); ++i) {
     auto c = static_cast<int>(binToStr.buf_.at(i));
-    if (c != 0 || i != binToStr.buf_.size() - 1) {
-      if (!std::isprint(static_cast<unsigned char>(c))) {
+    const bool bTrailingNull = c == 0 && i == binToStr.buf_.size() - 1;
+    if (!bTrailingNull) {
+      if (c < ' ' || c >= 127) {
         c = '.';
       }
       stream.put(static_cast<char>(c));