diff --git a/src/engine.rs b/src/engine.rs
index 0fa2ee9f..44cd129a 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -125,15 +125,23 @@ impl Imports {
     /// Does the specified function hash key exist in this stack of imported [modules][Module]?
     #[allow(dead_code)]
     pub fn contains_fn(&self, hash: u64) -> bool {
-        self.0.as_ref().map_or(false, |x| {
-            x.iter().any(|(_, m)| m.contains_qualified_fn(hash))
-        })
+        if hash == 0 {
+            false
+        } else {
+            self.0.as_ref().map_or(false, |x| {
+                x.iter().any(|(_, m)| m.contains_qualified_fn(hash))
+            })
+        }
     }
     /// Get specified function via its hash key.
     pub fn get_fn(&self, hash: u64) -> Option<&CallableFunction> {
-        self.0
-            .as_ref()
-            .and_then(|x| x.iter().rev().find_map(|(_, m)| m.get_qualified_fn(hash)))
+        if hash == 0 {
+            None
+        } else {
+            self.0
+                .as_ref()
+                .and_then(|x| x.iter().rev().find_map(|(_, m)| m.get_qualified_fn(hash)))
+        }
     }
     /// Does the specified [`TypeId`][std::any::TypeId] iterator exist in this stack of imported [modules][Module]?
     #[allow(dead_code)]
diff --git a/src/fn_call.rs b/src/fn_call.rs
index 82673b20..bb8720cb 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -443,8 +443,8 @@ impl Engine {
         // NOTE: We skip script functions for global_namespace and packages, and native functions for lib
 
         // First check script-defined functions
-        lib.iter().any(|&m| m.contains_fn(hash_script, pub_only))
-            //|| lib.iter().any(|&m| m.contains_fn(hash_fn, pub_only))
+        (hash_script != 0 && lib.iter().any(|&m| m.contains_fn(hash_script, pub_only)))
+            //|| (hash_fn != 0 && lib.iter().any(|&m| m.contains_fn(hash_fn, pub_only)))
             // Then check registered functions
             //|| self.global_namespace.contains_fn(hash_script, pub_only)
             || self.global_namespace.contains_fn(hash_fn, false)
diff --git a/src/packages/mod.rs b/src/packages/mod.rs
index bc764554..ca42cced 100644
--- a/src/packages/mod.rs
+++ b/src/packages/mod.rs
@@ -64,15 +64,23 @@ impl PackagesCollection {
     /// Does the specified function hash key exist in the [`PackagesCollection`]?
     #[allow(dead_code)]
     pub fn contains_fn(&self, hash: u64) -> bool {
-        self.0
-            .as_ref()
-            .map_or(false, |x| x.iter().any(|p| p.contains_fn(hash, false)))
+        if hash == 0 {
+            false
+        } else {
+            self.0
+                .as_ref()
+                .map_or(false, |x| x.iter().any(|p| p.contains_fn(hash, false)))
+        }
     }
     /// Get specified function via its hash key.
     pub fn get_fn(&self, hash: u64) -> Option<&CallableFunction> {
-        self.0
-            .as_ref()
-            .and_then(|x| x.iter().find_map(|p| p.get_fn(hash, false)))
+        if hash == 0 {
+            None
+        } else {
+            self.0
+                .as_ref()
+                .and_then(|x| x.iter().find_map(|p| p.get_fn(hash, false)))
+        }
     }
     /// Does the specified [`TypeId`] iterator exist in the [`PackagesCollection`]?
     #[allow(dead_code)]
diff --git a/src/parser.rs b/src/parser.rs
index f0003abd..946f9653 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -357,6 +357,7 @@ fn parse_fn_call(
             return Ok(Expr::FnCall(
                 Box::new(FnCallExpr {
                     name: id.to_string().into(),
+                    native_only: !is_valid_identifier(id.chars()), // script functions can only be valid identifiers
                     capture,
                     namespace,
                     hash: hash_script,
@@ -404,6 +405,7 @@ fn parse_fn_call(
                 return Ok(Expr::FnCall(
                     Box::new(FnCallExpr {
                         name: id.to_string().into(),
+                        native_only: !is_valid_identifier(id.chars()), // script functions can only be valid identifiers
                         capture,
                         namespace,
                         hash: hash_script,