diff --git a/Facade.h b/Facade.h
index 60e15f3..ffefbb3 100644
--- a/Facade.h
+++ b/Facade.h
@@ -2,6 +2,7 @@
 
 #include "VersionedMap.h"
 
+#include <assert.h>
 #include <map>
 #include <string>
 #include <vector>
@@ -133,7 +134,8 @@ struct Facade {
     for (auto iter = versioned.begin(version), end = versioned.end(version);
          iter != end; ++iter) {
       auto m = *iter;
-      if (m.version < unversionedVersion) {
+      assert(m.version <= version);
+      if (m.version <= unversionedVersion) {
         continue;
       }
       switch (m.type) {