diff --git a/src/compile.c b/src/compile.c
index 6ac0006..97db9c6 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -58,6 +58,7 @@ bool compile_isop(char* string) {
 	else if (strcmp(string, "and") == 0) return true;
 	else if (strcmp(string, "or") == 0) return true;
 	else if (strcmp(string, "|") == 0) return true;
+	else if (strcmp(string, ":?") == 0) return true;
 
 	else return false;