diff --git a/common/common.c b/common/common.c
index c2766ccf..0af2d4da 100644
--- a/common/common.c
+++ b/common/common.c
@@ -3,6 +3,7 @@
 #include "arena.h"
 #include "futex.h"
 #include <stdatomic.h>
+#include <ctype.h>
 
 #ifdef _WIN32
 #define WIN32_LEAN_AND_MEAN
diff --git a/meta/dsl.lua b/meta/dsl.lua
index e93326e7..f7c8afff 100644
--- a/meta/dsl.lua
+++ b/meta/dsl.lua
@@ -76,6 +76,7 @@ end
 lines[#lines + 1] = "#include \"../emitter.h\""
 lines[#lines + 1] = "#include \"../tb_internal.h\""
 lines[#lines + 1] = "#include <string.h>"
+lines[#lines + 1] = "#include <ctype.h>"
 lines[#lines + 1] = ""
 
 function decl_type(n)