diff --git a/cmake/QtInternalTargets.cmake b/cmake/QtInternalTargets.cmake
index 16db6e4bf0..6940a367ac 100644
--- a/cmake/QtInternalTargets.cmake
+++ b/cmake/QtInternalTargets.cmake
@@ -58,8 +58,15 @@ function(qt_internal_set_warnings_are_errors_flags target)
             list(APPEND flags /WX)
         endif()
     endif()
-    set(add_flags "$<NOT:$<BOOL:$<TARGET_PROPERTY:QT_SKIP_WARNINGS_ARE_ERRORS>>>")
-    set(flags_generator_expression "$<${add_flags}:${flags}>")
+    set(warnings_are_errors_enabled_genex
+        "$<NOT:$<BOOL:$<TARGET_PROPERTY:QT_SKIP_WARNINGS_ARE_ERRORS>>>")
+
+    # Apprently qmake only adds -Werror to CXX and OBJCXX files, not C files. We have to do the
+    # same otherwise MinGW builds break when building 3rdparty\md4c\md4c.c (and probably on other
+    # platforms too).
+    set(cxx_only_genex "$<OR:$<COMPILE_LANGUAGE:CXX>,$<COMPILE_LANGUAGE:OBJCXX>>")
+    set(final_condition_genex "$<AND:${warnings_are_errors_enabled_genex},${cxx_only_genex}>")
+    set(flags_generator_expression "$<${final_condition_genex}:${flags}>")
     target_compile_options("${target}" INTERFACE "${flags_generator_expression}")
 endfunction()