diff --git a/include/simdutf_c.h b/include/simdutf_c.h
index 7cfc41e..f497e68 100644
--- include/simdutf_c.h
+++ include/simdutf_c.h
@@ -12,17 +12,26 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-#ifdef __has_include
-  #if __has_include(<uchar.h>)
-    #include <uchar.h>
-  #else // __has_include(<uchar.h>)
+/* For C API, we need consistent types across C and C++ compilation.
+   In C++, we use the built-in char16_t/char32_t types.
+   In C, we define them as uint16_t/uint32_t. */
+#ifdef __cplusplus
+  /* Undefine any previous macros to use C++ built-in types */
+  #ifdef char16_t
+    #undef char16_t
+  #endif
+  #ifdef char32_t
+    #undef char32_t
+  #endif
+#else
+  /* For C compilation, define as integer types */
+  #ifndef char16_t
     #define char16_t uint16_t
+  #endif
+  #ifndef char32_t
     #define char32_t uint32_t
-  #endif // __has_include(<uchar.h>)
-#else    // __has_include(<uchar.h>)
-  #define char16_t uint16_t
-  #define char32_t uint32_t
-#endif // __has_include
+  #endif
+#endif
 
 #ifdef __cplusplus
 extern "C" {