diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index 5e52df956..a5fa2a6ed 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -30,6 +30,7 @@
 #include <climits>
 #include <iostream>
 #include <iomanip>
+#include <cctype>
 
 //---------------------------------------------------------------------------