diff --git a/Tools/Source/TianoTools/Common/CommonLib.c b/Tools/Source/TianoTools/Common/CommonLib.c
index c07ffb9e45..77f49a7875 100644
--- a/Tools/Source/TianoTools/Common/CommonLib.c
+++ b/Tools/Source/TianoTools/Common/CommonLib.c
@@ -495,10 +495,14 @@ Returns:
 }
 
 #ifdef __GNUC__
-void strlwr(char *s)
+#ifndef __CYGWIN__
+char *strlwr(char *s)
 {
+  char *p = s;
   for(;*s;s++) {
     *s = tolower(*s);
   }
+  return p;
 }
 #endif
+#endif
diff --git a/Tools/Source/TianoTools/Common/CommonLib.h b/Tools/Source/TianoTools/Common/CommonLib.h
index 257f066936..63f77e4557 100644
--- a/Tools/Source/TianoTools/Common/CommonLib.h
+++ b/Tools/Source/TianoTools/Common/CommonLib.h
@@ -131,7 +131,9 @@ PrintGuidToBuffer (
 #define stricmp strcasecmp
 #define strnicmp strncasecmp
 #define strcmpi strcasecmp
-void strlwr(char *s);
+#ifndef __CYGWIN__
+char *strlwr(char *s);
+#endif
 #endif
 
 #endif