diff --git a/Python/compile.c b/Python/compile.c
index b92cb44..dd14023 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -3579,10 +3579,10 @@
         case AugStore:
             break;
         case Del: op = DELETE_DEREF; break;
-        case Param:
         default:
-            PyErr_SetString(PyExc_SystemError,
-                            "param invalid for deref variable");
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         ctx);
             return 0;
         }
         break;
@@ -3596,10 +3596,10 @@
         case AugLoad:
         case AugStore:
             break;
-        case Param:
         default:
-            PyErr_SetString(PyExc_SystemError,
-                            "param invalid for local variable");
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         ctx);
             return 0;
         }
         ADDOP_N(c, op, mangled, varnames);
@@ -3614,10 +3614,10 @@
         case AugLoad:
         case AugStore:
             break;
-        case Param:
         default:
-            PyErr_SetString(PyExc_SystemError,
-                            "param invalid for global variable");
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         ctx);
             return 0;
         }
         break;
@@ -3631,10 +3631,10 @@
         case AugLoad:
         case AugStore:
             break;
-        case Param:
         default:
-            PyErr_SetString(PyExc_SystemError,
-                            "param invalid for name variable");
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         ctx);
             return 0;
         }
         break;
@@ -5058,10 +5058,10 @@
         case Del:
             ADDOP_NAME(c, DELETE_ATTR, e->v.Attribute.attr, names);
             break;
-        case Param:
         default:
-            PyErr_SetString(PyExc_SystemError,
-                            "param invalid in attribute expression");
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         e->v.Attribute.ctx);
             return 0;
         }
         break;
@@ -5359,9 +5359,10 @@
         case AugStore:/* fall through to Store */
         case Store:   op = STORE_SUBSCR; break;
         case Del:     op = DELETE_SUBSCR; break;
-        case Param:
-            PyErr_SetString(PyExc_SystemError,
-                "param invalid in subscript expression");
+        default:
+            PyErr_Format(PyExc_SystemError,
+                         "expr_context kind %d should not be possible",
+                         ctx);
             return 0;
     }
     if (ctx == AugStore) {