diff --git a/mongoose.c b/mongoose.c
index 3174523a..fd390088 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -1645,6 +1645,7 @@ void mbuf_remove(struct mbuf *mb, size_t n) {
 /* Amalgamated: #include "common/mg_str.h" */
 /* Amalgamated: #include "common/platform.h" */
 
+#include <ctype.h>
 #include <stdlib.h>
 #include <string.h>