diff --git a/Tests/TestsWorkingDirectory/main.cxx b/Tests/TestsWorkingDirectory/main.cxx
index eacd7ee59..6c4802d4a 100644
--- a/Tests/TestsWorkingDirectory/main.cxx
+++ b/Tests/TestsWorkingDirectory/main.cxx
@@ -1,6 +1,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
+#include <ctype.h>
 
 #if defined(_WIN32) && (defined(_MSC_VER) || defined(__WATCOMC__) || defined(__BORLANDC__) || defined(__MINGW32__))