diff --git a/examples/nim_timer/rust_bindings/src/api.rs b/examples/nim_timer/rust_bindings/src/api.rs
index 009aa4b..960431e 100644
--- a/examples/nim_timer/rust_bindings/src/api.rs
+++ b/examples/nim_timer/rust_bindings/src/api.rs
@@ -12,6 +12,17 @@ struct FfiCallbackResult {
 
 type Pair = Arc<(Mutex<FfiCallbackResult>, Condvar)>;
 
+/// Null-safe conversion from a C string returned by the Nim side.
+/// The C ABI permits a null `msg` even though the current producer
+/// always passes a non-null pointer; treat null as an empty string.
+unsafe fn cstr_to_string(msg: *const c_char) -> String {
+    if msg.is_null() {
+        String::new()
+    } else {
+        CStr::from_ptr(msg).to_string_lossy().into_owned()
+    }
+}
+
 unsafe extern "C" fn on_result(
     ret: c_int,
     msg: *const c_char,
@@ -21,11 +32,8 @@ unsafe extern "C" fn on_result(
     let pair = Arc::from_raw(user_data as *const (Mutex<FfiCallbackResult>, Condvar));
     let (lock, cvar) = &*pair;
     let mut state = lock.lock().unwrap();
-    state.payload = Some(if ret == 0 {
-        Ok(CStr::from_ptr(msg).to_string_lossy().into_owned())
-    } else {
-        Err(CStr::from_ptr(msg).to_string_lossy().into_owned())
-    });
+    let s = cstr_to_string(msg);
+    state.payload = Some(if ret == 0 { Ok(s) } else { Err(s) });
     cvar.notify_one();
 }
 
@@ -60,11 +68,8 @@ unsafe extern "C" fn on_result_async(
     let tx = Box::from_raw(
         user_data as *mut tokio::sync::oneshot::Sender<Result<String, String>>,
     );
-    let value = if ret == 0 {
-        Ok(CStr::from_ptr(msg).to_string_lossy().into_owned())
-    } else {
-        Err(CStr::from_ptr(msg).to_string_lossy().into_owned())
-    };
+    let s = cstr_to_string(msg);
+    let value = if ret == 0 { Ok(s) } else { Err(s) };
     let _ = tx.send(value);
 }
 
diff --git a/ffi/codegen/rust.nim b/ffi/codegen/rust.nim
index 28e265f..d489e41 100644
--- a/ffi/codegen/rust.nim
+++ b/ffi/codegen/rust.nim
@@ -258,6 +258,17 @@ proc generateApiRs*(procs: seq[FFIProcMeta], libName: string): string =
   lines.add("")
   lines.add("type Pair = Arc<(Mutex<FfiCallbackResult>, Condvar)>;")
   lines.add("")
+  lines.add("/// Null-safe conversion from a C string returned by the Nim side.")
+  lines.add("/// The C ABI permits a null `msg` even though the current producer")
+  lines.add("/// always passes a non-null pointer; treat null as an empty string.")
+  lines.add("unsafe fn cstr_to_string(msg: *const c_char) -> String {")
+  lines.add("    if msg.is_null() {")
+  lines.add("        String::new()")
+  lines.add("    } else {")
+  lines.add("        CStr::from_ptr(msg).to_string_lossy().into_owned()")
+  lines.add("    }")
+  lines.add("}")
+  lines.add("")
   lines.add("unsafe extern \"C\" fn on_result(")
   lines.add("    ret: c_int,")
   lines.add("    msg: *const c_char,")
@@ -267,11 +278,8 @@ proc generateApiRs*(procs: seq[FFIProcMeta], libName: string): string =
   lines.add("    let pair = Arc::from_raw(user_data as *const (Mutex<FfiCallbackResult>, Condvar));")
   lines.add("    let (lock, cvar) = &*pair;")
   lines.add("    let mut state = lock.lock().unwrap();")
-  lines.add("    state.payload = Some(if ret == 0 {")
-  lines.add("        Ok(CStr::from_ptr(msg).to_string_lossy().into_owned())")
-  lines.add("    } else {")
-  lines.add("        Err(CStr::from_ptr(msg).to_string_lossy().into_owned())")
-  lines.add("    });")
+  lines.add("    let s = cstr_to_string(msg);")
+  lines.add("    state.payload = Some(if ret == 0 { Ok(s) } else { Err(s) });")
   lines.add("    cvar.notify_one();")
   lines.add("}")
   lines.add("")
@@ -311,11 +319,8 @@ proc generateApiRs*(procs: seq[FFIProcMeta], libName: string): string =
   lines.add("    let tx = Box::from_raw(")
   lines.add("        user_data as *mut tokio::sync::oneshot::Sender<Result<String, String>>,")
   lines.add("    );")
-  lines.add("    let value = if ret == 0 {")
-  lines.add("        Ok(CStr::from_ptr(msg).to_string_lossy().into_owned())")
-  lines.add("    } else {")
-  lines.add("        Err(CStr::from_ptr(msg).to_string_lossy().into_owned())")
-  lines.add("    };")
+  lines.add("    let s = cstr_to_string(msg);")
+  lines.add("    let value = if ret == 0 { Ok(s) } else { Err(s) };")
   lines.add("    let _ = tx.send(value);")
   lines.add("}")
   lines.add("")