diff --git a/src/include/janet.h b/src/include/janet.h
index 146676f1..8968987b 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -322,7 +322,8 @@ typedef enum JanetType {
 #define JANET_TFLAG_INDEXED (JANET_TFLAG_ARRAY | JANET_TFLAG_TUPLE)
 #define JANET_TFLAG_DICTIONARY (JANET_TFLAG_TABLE | JANET_TFLAG_STRUCT)
 #define JANET_TFLAG_LENGTHABLE (JANET_TFLAG_BYTES | JANET_TFLAG_INDEXED | JANET_TFLAG_DICTIONARY)
-#define JANET_TFLAG_CALLABLE (JANET_TFLAG_FUNCTION | JANET_TFLAG_CFUNCTION | JANET_TFLAG_LENGTHABLE)
+#define JANET_TFLAG_CALLABLE (JANET_TFLAG_FUNCTION | JANET_TFLAG_CFUNCTION | \
+        JANET_TFLAG_LENGTHABLE | JANET_TFLAG_ABSTRACT)
 
 /* We provide three possible implementations of Janets. The preferred
  * nanboxing approach, for 32 or 64 bits, and the standard C version. Code in the rest of the