diff --git a/actix-prost-build/src/conversions.rs b/actix-prost-build/src/conversions.rs
index 62cef5e..d451d7c 100644
--- a/actix-prost-build/src/conversions.rs
+++ b/actix-prost-build/src/conversions.rs
@@ -365,6 +365,21 @@ impl ConversionsGenerator {
             Kind::Message(m) => Some(m),
             _ => None,
         }?;
+        let map_key_rust_type = match map_type.map_entry_key_field().kind() {
+            Kind::String => quote!(::prost::alloc::string::String),
+            Kind::Int32 => quote!(i32),
+            Kind::Int64 => quote!(i64),
+            Kind::Uint32 => quote!(u32),
+            Kind::Uint64 => quote!(u64),
+            Kind::Sint32 => quote!(i32),
+            Kind::Sint64 => quote!(i64),
+            Kind::Fixed32 => quote!(u32),
+            Kind::Fixed64 => quote!(u64),
+            Kind::Sfixed32 => quote!(i32),
+            Kind::Sfixed64 => quote!(i64),
+            Kind::Bool => quote!(bool),
+            _ => panic!("Map key type not supported"),
+        };
         // TODO: Proto name might not be the same as Rust struct name
         let rust_struct_name = self.messages.get(map_value_type.name())?.ident.clone();
 
@@ -379,7 +394,7 @@ impl ConversionsGenerator {
         } else {
             panic!("Type of map field is not a path")
         };
-        let ty = quote!(#map_collection<String, #new_struct_name>);
+        let ty = quote!(#map_collection<#map_key_rust_type, #new_struct_name>);
         let conversion = quote!(#convert::try_convert(from.#name)?);
         Some((ty, conversion))
     }
diff --git a/tests/src/proto/conversions.rs b/tests/src/proto/conversions.rs
index 693a857..3e6190e 100644
--- a/tests/src/proto/conversions.rs
+++ b/tests/src/proto/conversions.rs
@@ -160,7 +160,10 @@ impl convert_trait::TryConvert<Nested> for NestedInternal {
 }
 #[derive(Debug)]
 pub struct ConversionsRequestInternal {
-    pub map_field: ::std::collections::HashMap<String, MapValueInternal>,
+    pub map_field: ::std::collections::HashMap<
+        ::prost::alloc::string::String,
+        MapValueInternal,
+    >,
     pub query: ::prost::alloc::string::String,
     pub addresses: std::collections::HashSet<ethers::types::Address>,
     pub nested_enum: conversions_request::NestedEnum,
@@ -201,7 +204,10 @@ impl convert_trait::TryConvert<MapValueInternal> for MapValue {
 pub struct ConversionsResponseInternal {
     pub address: ethers::types::Address,
     pub nested: ::core::option::Option<NestedInternal>,
-    pub map_field: ::std::collections::HashMap<String, MapValueInternal>,
+    pub map_field: ::std::collections::HashMap<
+        ::prost::alloc::string::String,
+        MapValueInternal,
+    >,
 }
 impl convert_trait::TryConvert<ConversionsResponseInternal> for ConversionsResponse {
     fn try_convert(from: ConversionsResponseInternal) -> Result<Self, String> {