diff --git a/VersionedMap.cpp b/VersionedMap.cpp
index 125e24c..8303749 100644
--- a/VersionedMap.cpp
+++ b/VersionedMap.cpp
@@ -263,7 +263,7 @@ struct MemManager {
     if (next == firstUnaddressable) {
       mprotectSafe(base + firstUnaddressable, kUpsizeBytes,
                    PROT_READ | PROT_WRITE);
-      VALGRIND_MAKE_MEM_UNDEFINED(base + firstUnaddressable, kUpsizeBytes);
+      VALGRIND_MAKE_MEM_NOACCESS(base + firstUnaddressable, kUpsizeBytes);
       firstUnaddressable += kUpsizeNodes;
 #if SHOW_MEMORY
       mmapBytes = getBytes();
@@ -278,6 +278,7 @@ struct MemManager {
       }
     }
 
+    VALGRIND_MAKE_MEM_UNDEFINED(base + next, sizeof(Node));
     return next++;
   }
 
@@ -1682,4 +1683,4 @@ int main() {
 }
 #endif
 
-// GCOVR_EXCL_STOP
\ No newline at end of file
+// GCOVR_EXCL_STOP