diff --git a/src/gr/nmod32.c b/src/gr/nmod32.c
index d27745411e..65e73ae488 100644
--- a/src/gr/nmod32.c
+++ b/src/gr/nmod32.c
@@ -306,7 +306,7 @@ _nmod32_vec_dot(nmod32_t res, const nmod32_t initial, int subtract, const nmod32
     else
     {
         if (subtract)
-            s = (n - initial[0]);
+            s = n_negmod(initial[0], n);
         else
             s = initial[0];
     }
@@ -353,7 +353,7 @@ _nmod32_vec_dot_rev(nmod32_t res, const nmod32_t initial, int subtract, const nm
     else
     {
         if (subtract)
-            s = (n - initial[0]);
+            s = n_negmod(initial[0], n);
         else
             s = initial[0];
     }
diff --git a/src/gr/nmod8.c b/src/gr/nmod8.c
index 0e6260a1b0..fb6d0e8d78 100644
--- a/src/gr/nmod8.c
+++ b/src/gr/nmod8.c
@@ -305,7 +305,7 @@ _nmod8_vec_dot(nmod8_t res, const nmod8_t initial, int subtract, const nmod8_str
     else
     {
         if (subtract)
-            s = (n - initial[0]);
+            s = n_negmod(initial[0], n);
         else
             s = initial[0];
     }
@@ -370,7 +370,7 @@ _nmod8_vec_dot_rev(nmod8_t res, const nmod8_t initial, int subtract, const nmod8
     else
     {
         if (subtract)
-            s = (n - initial[0]);
+            s = n_negmod(initial[0], n);
         else
             s = initial[0];
     }