diff --git a/mandel.s b/mandel.s
index 1244a02..3622995 100644
--- a/mandel.s
+++ b/mandel.s
@@ -344,18 +344,6 @@ fill_masks:
     neg 4, arg
 .endmacro
 
-; 5 to 25 cycles
-.macro check_sign arg
-    ; Check sign bit and flip argument to postive,
-    ; keeping a count of sign bits in the Y register.
-    .local positive
-    lda arg + 1   ; 3 cyc
-    bpl positive  ; 2 cyc
-    neg16 arg     ; 18 cyc
-    iny           ; 2 cyc
-positive:
-.endmacro
-
 ; 518 - 828 cyc
 .macro imul16 dest, arg1, arg2
     copy16 FR0, arg1  ; 12 cyc
@@ -438,11 +426,6 @@ positive:
     result = FR2 ; 32-bit result
     inter = temp2
 
-    ldy #0          ; 2 cyc
-    ; counts the number of sign bits in Y
-    check_sign arg1 ; 5 to 25 cyc
-    check_sign arg2 ; 5 to 25 cyc
-
     ; h1l1 * h2l2
     ; (h1*256 + l1) * (h2*256 + l2)
     ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
@@ -464,11 +447,16 @@ positive:
     imul8 inter, arg1 + 1, arg2 + 1
     add16 result + 2, result + 2, inter
 
-    ; In case of mixed input signs, return a negative result.
-    cpy #1              ; 2 cyc
-    bne positive_result ; 2 cyc
-    neg32 result        ; 34 cyc
-positive_result:
+    ; In case of negative inputs, adjust high word
+    ; https://stackoverflow.com/a/28827013
+    lda arg1 + 1
+    bpl arg1_pos
+    sub16 result + 2, result + 2, arg2
+arg1_pos:
+    lda arg2 + 1
+    bpl arg2_pos
+    sub16 result + 2, result + 2, arg1
+arg2_pos:
 
     rts ; 6 cyc
 .endproc