diff --git a/prost-build/src/code_generator.rs b/prost-build/src/code_generator.rs
index 4f348baaf..ecd21852a 100644
--- a/prost-build/src/code_generator.rs
+++ b/prost-build/src/code_generator.rs
@@ -122,18 +122,7 @@ impl<'a> CodeGenerator<'a> {
         debug!("  message: {:?}", message.name());
 
         let message_name = message.name().to_string();
-        let fq_message_name = format!(
-            "{}{}{}{}.{}",
-            if self.package.is_empty() && self.type_path.is_empty() {
-                ""
-            } else {
-                "."
-            },
-            self.package.trim_matches('.'),
-            if self.type_path.is_empty() { "" } else { "." },
-            self.type_path.join("."),
-            message_name,
-        );
+        let fq_message_name = self.fq_name(&message_name);
 
         // Skip external types.
         if self.extern_paths.resolve_ident(&fq_message_name).is_some() {
@@ -701,18 +690,7 @@ impl<'a> CodeGenerator<'a> {
         let enum_name = to_upper_camel(proto_enum_name);
 
         let enum_values = &desc.value;
-        let fq_proto_enum_name = format!(
-            "{}{}{}{}.{}",
-            if self.package.is_empty() && self.type_path.is_empty() {
-                ""
-            } else {
-                "."
-            },
-            self.package.trim_matches('.'),
-            if self.type_path.is_empty() { "" } else { "." },
-            self.type_path.join("."),
-            proto_enum_name,
-        );
+        let fq_proto_enum_name = self.fq_name(proto_enum_name);
 
         if self
             .extern_paths
@@ -1065,6 +1043,18 @@ impl<'a> CodeGenerator<'a> {
             .as_ref()
             .map_or(false, FieldOptions::deprecated)
     }
+
+    /// Returns the fully-qualified name, starting with a dot
+    fn fq_name(&self, message_name: &str) -> String {
+        format!(
+            "{}{}{}{}.{}",
+            if self.package.is_empty() { "" } else { "." },
+            self.package.trim_matches('.'),
+            if self.type_path.is_empty() { "" } else { "." },
+            self.type_path.join("."),
+            message_name,
+        )
+    }
 }
 
 /// Returns `true` if the repeated field type can be packed.
diff --git a/tests/src/build.rs b/tests/src/build.rs
index aec3f6458..e2b95e6c4 100644
--- a/tests/src/build.rs
+++ b/tests/src/build.rs
@@ -111,6 +111,10 @@ fn main() {
         .compile_protos(&[src.join("option_struct.proto")], includes)
         .unwrap();
 
+    config
+        .compile_protos(&[src.join("submessage_without_package.proto")], includes)
+        .unwrap();
+
     prost_build::Config::new()
         .protoc_arg("--experimental_allow_proto3_optional")
         .compile_protos(&[src.join("proto3_presence.proto")], includes)
diff --git a/tests/src/lib.rs b/tests/src/lib.rs
index 954c6b367..b95f2d77a 100644
--- a/tests/src/lib.rs
+++ b/tests/src/lib.rs
@@ -46,6 +46,8 @@ mod no_unused_results;
 #[cfg(feature = "std")]
 mod skip_debug;
 #[cfg(test)]
+mod submessage_without_package;
+#[cfg(test)]
 mod type_names;
 
 mod test_enum_named_option_value {
diff --git a/tests/src/submessage_without_package.proto b/tests/src/submessage_without_package.proto
new file mode 100644
index 000000000..c637b29bc
--- /dev/null
+++ b/tests/src/submessage_without_package.proto
@@ -0,0 +1,8 @@
+syntax = "proto3";
+
+message M {
+  message SubMessage {
+    map<string, string> item = 1;
+  }
+  SubMessage reply = 2;
+}
diff --git a/tests/src/submessage_without_package.rs b/tests/src/submessage_without_package.rs
new file mode 100644
index 000000000..8f02a26e6
--- /dev/null
+++ b/tests/src/submessage_without_package.rs
@@ -0,0 +1,6 @@
+include!(concat!(env!("OUT_DIR"), "/_.rs"));
+
+#[test]
+fn test_submessage_without_package() {
+    let _msg = M::default();
+}