diff --git a/JsonPreprocessor/CJsonPreprocessor.py b/JsonPreprocessor/CJsonPreprocessor.py
index 4989acc..1cf0183 100644
--- a/JsonPreprocessor/CJsonPreprocessor.py
+++ b/JsonPreprocessor/CJsonPreprocessor.py
@@ -2148,6 +2148,23 @@ def __handleLastElement(sInput : str) -> str:
                 self.__reset()
                 raise Exception(f"{error} in line: '{line}'")
             line = line.rstrip()
+            # Check for Python inline code on left-hand side of colon (not allowed)
+            if '<<' in line and ':' in line:
+                # Check if any Python inline code pattern appears before any colon on the line
+                # This catches all forms: <<...>>, "<<...>>", ${<<...>>}, param[<<...>>], etc.
+                # Split by colon and check if left parts contain Python inline code
+                parts = line.split(':')
+                for i in range(len(parts) - 1):  # All parts except the last could be key parts
+                    left_part = parts[i]
+                    if regex.search(r'<<.*?>>', left_part):
+                        # Additional check: make sure this looks like a key part, not a value part
+                        # Skip if this part seems to be continuing a previous value
+                        stripped_left = left_part.strip()
+                        # Simple heuristic: if it starts with a quote, comma, or common key patterns, it's likely a key
+                        if (stripped_left.startswith(('"', "'", '${', ',')) or 
+                            regex.search(r'[{,]\s*[^,}]*$', stripped_left)):
+                            self.__reset()
+                            raise Exception("Python inline code on the left-hand side of the colon is generally not allowed.")
             # Checks the syntax of the Python inline code
             if '<<' in line or '>>' in line:
                 patterns = [