diff --git a/mlir/include/mlir/Bindings/Python/PybindAdaptors.h b/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
--- a/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
+++ b/mlir/include/mlir/Bindings/Python/PybindAdaptors.h
@@ -42,13 +42,19 @@
 /// an explicit Capsule (which can happen when two C APIs are communicating
 /// directly via Python) or indirectly by querying the MLIR_PYTHON_CAPI_PTR_ATTR
 /// attribute (through which supported MLIR Python API objects export their
-/// contained API pointer as a capsule). This is intended to be used from
-/// type casters, which are invoked with a raw handle (unowned). The returned
-/// object's lifetime may not extend beyond the apiObject handle without
-/// explicitly having its refcount increased (i.e. on return).
+/// contained API pointer as a capsule). Throws a type error if the object is
+/// neither. This is intended to be used from type casters, which are invoked
+/// with a raw handle (unowned). The returned object's lifetime may not extend
+/// beyond the apiObject handle without explicitly having its refcount increased
+/// (i.e. on return).
 static py::object mlirApiObjectToCapsule(py::handle apiObject) {
   if (PyCapsule_CheckExact(apiObject.ptr()))
     return py::reinterpret_borrow<py::object>(apiObject);
+  if (!py::hasattr(apiObject, MLIR_PYTHON_CAPI_PTR_ATTR)) {
+    auto repr = py::repr(apiObject).cast<std::string>();
+    throw py::type_error(
+        (llvm::Twine("Expected an MLIR object (got ") + repr + ").").str());
+  }
   return apiObject.attr(MLIR_PYTHON_CAPI_PTR_ATTR);
 }
 
diff --git a/mlir/test/python/dialects/python_test.py b/mlir/test/python/dialects/python_test.py
--- a/mlir/test/python/dialects/python_test.py
+++ b/mlir/test/python/dialects/python_test.py
@@ -247,6 +247,15 @@
     else:
       raise
 
+    # The following must trigger a TypeError from our adaptors and must not
+    # crash.
+    try:
+      test.TestAttr(42)
+    except TypeError as e:
+      assert "Expected an MLIR object" in str(e)
+    else:
+      raise
+
     # The following must trigger a TypeError from pybind (therefore, not
     # checking its message) and must not crash.
     try:
@@ -276,6 +285,15 @@
     else:
       raise
 
+    # The following must trigger a TypeError from our adaptors and must not
+    # crash.
+    try:
+      test.TestType(42)
+    except TypeError as e:
+      assert "Expected an MLIR object" in str(e)
+    else:
+      raise
+
     # The following must trigger a TypeError from pybind (therefore, not
     # checking its message) and must not crash.
     try: