diff --git a/icu4c/source/test/cintltst/cintltst.h b/icu4c/source/test/cintltst/cintltst.h
index 0deccd8c72a..952a8695aa1 100644
--- a/icu4c/source/test/cintltst/cintltst.h
+++ b/icu4c/source/test/cintltst/cintltst.h
@@ -42,7 +42,7 @@ U_CFUNC const char* ctest_dataOutDir(void);
  */
 U_CFUNC void ctest_pathnameInContext(char* fullname, int32_t maxsize, const char* relPath ) ;
 
-UChar* CharsToUChars(const char* chars);
+U_CFUNC UChar* CharsToUChars(const char* chars);
 
 /**
  * Convert a const UChar* into a char*