diff --git a/lib/src/invocation_matcher.dart b/lib/src/invocation_matcher.dart
index 005eb05..d809c19 100644
--- a/lib/src/invocation_matcher.dart
+++ b/lib/src/invocation_matcher.dart
@@ -171,6 +171,11 @@
     if (e2 is Matcher && e1 is! Matcher) {
       return e2.matches(e1, {});
     }
+    // If one thing is a `SmartFake` but not the other, always fail.
+    // Otherwise the real thing might try calling private members on
+    // fake, and that fails at runtime with confusing errors.
+    if ((e1 is SmartFake) ^ (e2 is SmartFake)) return false;
+
     return super.equals(e1, e2);
   }