diff --git a/mandel.s b/mandel.s
index 7242596..30ed07d 100644
--- a/mandel.s
+++ b/mandel.s
@@ -361,32 +361,33 @@ positive_result:
     ; Round top 16 bits of 32-bit fixed-point number in-place
     .local positive
     .local negative
-    .local increment
+    .local no_carry
     .local next
 
     ; positive input:
-    ;   0 rounds down, no change - 10 cyc
-    ;   1 rounds up, add one - 17-22 cyc
+    ;   0 rounds down, no change - 5 cyc
+    ;   1 rounds up, add one - 15-20 cyc
     ; negative input:
-    ;   0 rounds up, add one - 19-24 cyc
-    ;   1 rounds down, no change - 10 cyc
+    ;   0 rounds up, no change - 5 cyc
+    ;   1 rounds down, sub one - 23-28 cyc
+
+    ; check 16th bit down
+    lda arg + 1   ; 3 cyc
+    bpl next      ; 2 cyc
 
     ; check sign bit
     lda arg + 3  ; 3 cyc
     bpl positive ; 2 cyc
 
-negative:
-    ; check 16th bit down
-    lda arg + 1   ; 3 cyc
-    bmi next      ; 2 cyc
-    bpl increment ; 2 cyc
+negative:        ; 13-18 cyc
+    lda arg + 2  ; 3 cyc
+    bne no_carry ; 2 cyc
+    dec arg + 3  ; 5 cyc
+no_carry:
+    dec arg + 2  ; 5 cyc
+    jmp next     ; 3 cyc
 
-positive:
-    ; check 16th bit down
-    lda arg + 1   ; 3 cyc
-    bpl next      ; 2 cyc
-
-increment:
+positive:        ; 5-10 cyc
     inc arg + 2  ; 5 cyc
     bne next     ; 2 cyc
     inc arg + 3  ; 5 cyc