diff --git a/reflect/protoregistry/registry.go b/reflect/protoregistry/registry.go
index 3c7ec70..59f024c 100644
--- a/reflect/protoregistry/registry.go
+++ b/reflect/protoregistry/registry.go
@@ -121,8 +121,13 @@
 		r.filesByPath = make(map[string][]protoreflect.FileDescriptor)
 	}
 	path := file.Path()
-	if len(r.filesByPath[path]) > 0 {
+	if prev := r.filesByPath[path]; len(prev) > 0 {
 		r.checkGenProtoConflict(path)
+		err := errors.New("file %q is already registered", file.Path())
+		err = amendErrorWithCaller(err, prev[0], file)
+		if !(r == GlobalFiles && ignoreConflict(file, err)) {
+			return err
+		}
 	}
 
 	for name := file.Package(); name != ""; name = name.Parent() {
diff --git a/reflect/protoregistry/registry_test.go b/reflect/protoregistry/registry_test.go
index bc8019c..d058c19 100644
--- a/reflect/protoregistry/registry_test.go
+++ b/reflect/protoregistry/registry_test.go
@@ -69,7 +69,7 @@
 		files: []testFile{
 			{inFile: mustMakeFile(`syntax:"proto2" name:"test1.proto" package:"foo.bar"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"my.test"`)},
-			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"foo.bar.baz"`)},
+			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"foo.bar.baz"`), wantErr: "already registered"},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"test2.proto" package:"my.test.package"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"weird" package:"foo.bar"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/baz/../test.proto" package:"my.test"`)},
@@ -112,8 +112,10 @@
 				{"weird", "foo.bar"},
 			},
 		}, {
-			inPath:  "foo/bar/test.proto",
-			wantErr: `multiple files named "foo/bar/test.proto"`,
+			inPath: "foo/bar/test.proto",
+			wantFiles: []file{
+				{"foo/bar/test.proto", "my.test"},
+			},
 		}},
 	}, {
 		// Test when new enum conflicts with existing package.