diff --git a/spec/std/enumerable_spec.cr b/spec/std/enumerable_spec.cr
index 5c66ddf55062..09d89ddcdf6d 100644
--- a/spec/std/enumerable_spec.cr
+++ b/spec/std/enumerable_spec.cr
@@ -1374,8 +1374,8 @@ describe "Enumerable" do
         [1, 10000000000_u64].sum
         CRYSTAL
         "Enumerable#sum() and #product() do not support Union types. " +
-        "Instead, use Enumerable#sum and #product(initial), respectively, " +
-        "with an initial value of the intended type of the call."
+        "Instead, use Enumerable#sum(initial) and #product(initial), " +
+        "respectively, with an initial value of the intended type of the call."
     end
 
     it "uses additive_identity from type" do
@@ -1428,8 +1428,8 @@ describe "Enumerable" do
         [1, 10000000000_u64].product
         CRYSTAL
         "Enumerable#sum() and #product() do not support Union types. " +
-        "Instead, use Enumerable#sum and #product(initial), respectively, " +
-        "with an initial value of the intended type of the call."
+        "Instead, use Enumerable#sum(initial) and #product(initial), " +
+        "respectively, with an initial value of the intended type of the call."
     end
   end
 
diff --git a/src/enumerable.cr b/src/enumerable.cr
index fb78d5c569ce..0e87867b28dd 100644
--- a/src/enumerable.cr
+++ b/src/enumerable.cr
@@ -2300,7 +2300,7 @@ module Enumerable(T)
       {% if X.union? %}
         {{
           raise("Enumerable#sum() and #product() do not support Union types. " +
-                "Instead, use Enumerable#sum and #product(initial), " +
+                "Instead, use Enumerable#sum(initial) and #product(initial), " +
                 "respectively, with an initial value of the intended type " +
                 "of the call.")
         }}