# sympy__sympy-13773
# Loki Mode Multi-Agent Patch
# Attempts: 1

This is a standalone patch request for the SymPy repository. I need to generate the patch based on my knowledge of the SymPy codebase structure. Let me search for information about how the SymPy Matrix `__matmul__` is typically implemented.

Based on my knowledge of SymPy's codebase structure and the architect's analysis, I can generate the appropriate patch. The `__matmul__` and `__rmatmul__` methods are in `sympy/matrices/common.py` within the `MatrixArithmetic` class.

```
--- a/sympy/matrices/common.py
+++ b/sympy/matrices/common.py
@@ -1973,10 +1973,26 @@ class MatrixArithmetic(MatrixRequired):
             return self._eval_scalar_rmul(other)
 
     @call_highest_priority('__rmatmul__')
     def __matmul__(self, other):
-        return self.__mul__(other)
+        other = _matrixify(other)
+        if not getattr(other, 'is_Matrix', False):
+            raise ValueError("Scalar operands are not allowed, use '*' instead")
+        return self.__mul__(other)
 
     @call_highest_priority('__matmul__')
     def __rmatmul__(self, other):
-        return self.__rmul__(other)
+        other = _matrixify(other)
+        if not getattr(other, 'is_Matrix', False):
+            raise ValueError("Scalar operands are not allowed, use '*' instead")
+        return self.__rmul__(other)
 
     @call_highest_priority('__mul__')
```