diff --git a/src/FbTk/ITypeAheadable.hh b/src/FbTk/ITypeAheadable.hh
index 4a5b7cc7..1b0bd035 100644
--- a/src/FbTk/ITypeAheadable.hh
+++ b/src/FbTk/ITypeAheadable.hh
@@ -24,6 +24,12 @@
 
 #include <string>
 
+#ifdef HAVE_CCTYPE
+  #include <cctype>
+#else
+  #include <ctype.h>
+#endif // HAVE_CCTYPE
+
 namespace FbTk {
 
 // abstract base class providing access and validation