diff --git a/src/mzscheme/src/jit.c b/src/mzscheme/src/jit.c
index 3567b51fe0..11a1abc0b4 100644
--- a/src/mzscheme/src/jit.c
+++ b/src/mzscheme/src/jit.c
@@ -1337,7 +1337,7 @@ static int generate_self_tail_call(Scheme_Object *rator, mz_jit_state *jitter, i
   /* Last argument is in R0 */
 
 #ifdef JIT_PRECISE_GC
-  closure_size++; /* Skip procedure pointer, too */
+  closure_size += 1; /* Skip procedure pointer, too */
 #endif
 
   __START_SHORT_JUMPS__(1);