diff --git a/regression-tests/pure2-bugfix-for-out-this-nonconstructor-error.cpp2 b/regression-tests/pure2-bugfix-for-out-this-nonconstructor-error.cpp2
new file mode 100644
index 000000000..6831e3675
--- /dev/null
+++ b/regression-tests/pure2-bugfix-for-out-this-nonconstructor-error.cpp2
@@ -0,0 +1,4 @@
+
+Machine: @polymorphic_base <I:int> type = {
+    operator%: (out this, _: std::string) = {}
+}
diff --git a/regression-tests/test-results/pure2-bugfix-for-out-this-nonconstructor-error.cpp2.output b/regression-tests/test-results/pure2-bugfix-for-out-this-nonconstructor-error.cpp2.output
new file mode 100644
index 000000000..0d5527d6d
--- /dev/null
+++ b/regression-tests/test-results/pure2-bugfix-for-out-this-nonconstructor-error.cpp2.output
@@ -0,0 +1,3 @@
+pure2-bugfix-for-out-this-nonconstructor-error.cpp2...
+pure2-bugfix-for-out-this-nonconstructor-error.cpp2(3,16): error: a function with an 'out this' parameter must be a constructor
+
diff --git a/source/parse.h b/source/parse.h
index 9c80447bf..922811b98 100644
--- a/source/parse.h
+++ b/source/parse.h
@@ -4502,9 +4502,10 @@ auto function_type_node::is_constructor() const
         (*parameters).ssize() > 0
         && (*parameters)[0]->has_name("this")
         && (*parameters)[0]->direction() == passing_style::out
+        && my_decl
+        && my_decl->has_name("operator=")
         )
     {
-        assert(my_decl && my_decl->has_name("operator="));
         return true;
     }
     return false;
diff --git a/source/sema.h b/source/sema.h
index 424261a69..9891913c1 100644
--- a/source/sema.h
+++ b/source/sema.h
@@ -2086,6 +2086,21 @@ class sema
             }
         }
 
+        //  If the first parameter is 'out this', it must be a constructor.
+        if (
+            !n.is_constructor()
+            && (*n.parameters).ssize() > 0
+            && (*n.parameters)[0]->has_name("this")
+            && (*n.parameters)[0]->direction() == passing_style::out
+            )
+        {
+            errors.emplace_back(
+                n.position(),
+                "a function with an 'out this' parameter must be a constructor"
+            );
+            return false;
+        }
+
         return true;
     }