diff --git a/bignum.c b/bignum.c
index 097aced1..48a71b84 100644
--- a/bignum.c
+++ b/bignum.c
@@ -999,8 +999,8 @@ sexp sexp_complex_sub (sexp ctx, sexp a, sexp b) {
   sexp_gc_var2(res, tmp);
   sexp_gc_preserve2(ctx, res, tmp);
   tmp = sexp_complex_copy(ctx, b);
-  sexp_negate(sexp_complex_real(tmp));
-  sexp_negate(sexp_complex_imag(tmp));
+  sexp_negate_maybe_ratio(sexp_complex_real(tmp));
+  sexp_negate_maybe_ratio(sexp_complex_imag(tmp));
   res = sexp_complex_add(ctx, a, tmp);
   sexp_gc_release2(ctx);
   return res;
@@ -1453,11 +1453,7 @@ sexp sexp_sub (sexp ctx, sexp a, sexp b) {
     sexp_negate_exact(sexp_ratio_numerator(tmp2));
     r = sexp_ratio_add(ctx, a, tmp2);
     if (negatep) {
-      if (sexp_ratiop(r)) {
-        sexp_negate_exact(sexp_ratio_numerator(r));
-      } else {
-        sexp_negate_exact(r);
-      }
+      sexp_negate_maybe_ratio(r);
     }
     break;
 #endif
@@ -1489,10 +1485,10 @@ sexp sexp_sub (sexp ctx, sexp a, sexp b) {
     if (negatep) {
       if (sexp_complexp(r)) {
         r = sexp_complex_copy(ctx, r);
-        sexp_negate(sexp_complex_real(r));
-        sexp_negate(sexp_complex_imag(r));
+        sexp_negate_maybe_ratio(sexp_complex_real(r));
+        sexp_negate_maybe_ratio(sexp_complex_imag(r));
       } else {
-        sexp_negate(r);
+        sexp_negate_maybe_ratio(r);
       }
     }
     break;
diff --git a/sexp.c b/sexp.c
index c0b65b69..4ae00bcf 100644
--- a/sexp.c
+++ b/sexp.c
@@ -3632,9 +3632,9 @@ sexp sexp_read_raw (sexp ctx, sexp in, sexp *shares) {
 #if SEXP_USE_COMPLEX
           if (sexp_complexp(res)) {
             if (sexp_complex_real(res) == SEXP_ZERO) {
-              sexp_negate(sexp_complex_imag(res));
+              sexp_negate_maybe_ratio(sexp_complex_imag(res));
             } else {
-              sexp_negate(sexp_complex_real(res));
+              sexp_negate_maybe_ratio(sexp_complex_real(res));
             }
           } else
 #endif
diff --git a/tests/r7rs-tests.scm b/tests/r7rs-tests.scm
index 602fc5c4..24f6e94f 100644
--- a/tests/r7rs-tests.scm
+++ b/tests/r7rs-tests.scm
@@ -889,6 +889,8 @@
 (test -1 (- 3 4))
 (test -6 (- 3 4 5))
 (test -3 (- 3))
+(test -3/2 (- 3/2))
+(test -3/2-i (- 3/2+i))
 (test 3/20 (/ 3 4 5))
 (test 1/3 (/ 3))