diff --git a/src/middlewares/methods/inject_params.rs b/src/middlewares/methods/inject_params.rs
index b07ecad..d645372 100644
--- a/src/middlewares/methods/inject_params.rs
+++ b/src/middlewares/methods/inject_params.rs
@@ -122,42 +122,44 @@ impl Middleware<CallRequest, CallResult> for InjectParamsMiddleware {
 
         let idx = self.get_index();
         match request.params.len() {
-            len if len == idx + 1 => {
-                // full params with current block
+            len if len > idx + 1 => {
+                // unexpected number of params
                 return handle_request(request).await;
             }
             len if len <= idx => {
-                async move {
-                    // without current block
-                    let to_inject = self.get_parameter().await;
-                    tracing::trace!("Injected param {} to method {}", &to_inject, request.method);
-                    let params_passed = request.params.len();
-                    while request.params.len() < idx {
-                        let current = request.params.len();
-                        if self.params[current].optional {
-                            request.params.push(JsonValue::Null);
-                        } else {
-                            let (required, optional) = self.params_count();
-                            return Err(errors::invalid_params(format!(
-                                "Expected {:?} parameters ({:?} optional), {:?} found instead",
-                                required + optional,
-                                optional,
-                                params_passed
-                            )));
-                        }
+                // without current block
+                let params_passed = request.params.len();
+                while request.params.len() < idx {
+                    let current = request.params.len();
+                    if self.params[current].optional {
+                        request.params.push(JsonValue::Null);
+                    } else {
+                        let (required, optional) = self.params_count();
+                        return Err(errors::invalid_params(format!(
+                            "Expected {:?} parameters ({:?} optional), {:?} found instead",
+                            required + optional,
+                            optional,
+                            params_passed
+                        )));
                     }
-                    request.params.push(to_inject);
-
-                    handle_request(request).await
                 }
-                .with_context(TRACER.context("inject_params"))
-                .await
+                // Set param to null, it will be replaced later
+                request.params.push(JsonValue::Null);
             }
-            _ => {
-                // unexpected number of params
-                handle_request(request).await
+            _ => {} // full params, block potentially might be null
+        };
+
+        // Here we are sure we have full params in the request, but it still might be set to null
+        async move {
+            if request.params[idx] == JsonValue::Null {
+                let to_inject = self.get_parameter().await;
+                tracing::trace!("Injected param {} to method {}", &to_inject, request.method);
+                request.params[idx] = to_inject;
             }
+            handle_request(request).await
         }
+        .with_context(TRACER.context("inject_params"))
+        .await
     }
 }
 
@@ -286,6 +288,44 @@ mod tests {
         assert_eq!(result, json!("0x1111"));
     }
 
+    #[tokio::test]
+    async fn inject_if_param_is_null() {
+        let params = vec![json!("0x1234"), json!(None::<()>)];
+        let (middleware, _) = create_inject_middleware(
+            InjectType::BlockHashAt(1),
+            vec![
+                MethodParam {
+                    name: "key".to_string(),
+                    ty: "StorageKey".to_string(),
+                    optional: false,
+                    inject: false,
+                },
+                MethodParam {
+                    name: "at".to_string(),
+                    ty: "BlockHash".to_string(),
+                    optional: true,
+                    inject: true,
+                },
+            ],
+        )
+        .await;
+        let result = middleware
+            .call(
+                CallRequest::new("state_getStorage", params.clone()),
+                Default::default(),
+                Box::new(move |req: CallRequest, _| {
+                    async move {
+                        assert_eq!(req.params, vec![json!("0x1234"), json!("0xabcd")]);
+                        Ok(json!("0x1111"))
+                    }
+                    .boxed()
+                }),
+            )
+            .await
+            .unwrap();
+        assert_eq!(result, json!("0x1111"));
+    }
+
     #[tokio::test]
     async fn inject_if_without_current_block_hash() {
         let (middleware, _context) = create_inject_middleware(