Try #432:

lib/runtime-c-api/src/error.rs

@@ -61,20 +61,20 @@ pub unsafe extern "C" fn wasmer_last_error_message(buffer: *mut c_char, length:
         return -1;
     }
 
-    let last_error = match take_last_error() {
-        Some(err) => err,
+    let error_message = match take_last_error() {
+        Some(err) => err.to_string(),
         None => return 0,
     };
 
-    let error_message = last_error.to_string();
+    let length = length as usize;
 
-    let buffer = slice::from_raw_parts_mut(buffer as *mut u8, length as usize);
-
-    if error_message.len() >= buffer.len() {
-        // buffer to small for err  message
+    if error_message.len() >= length {
+        // buffer to small to hold the error message
         return -1;
     }
 
+    let buffer = slice::from_raw_parts_mut(buffer as *mut u8, length);
+
     ptr::copy_nonoverlapping(
         error_message.as_ptr(),
         buffer.as_mut_ptr(),