diff --git a/.circleci/config.yml b/.circleci/config.yml
index 63780bca3..767c64248 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -135,7 +135,7 @@ jobs:
     steps:
       - pre-steps
       - install-gflags
-      - run: ASSERT_STATUS_CHECKED=1 TEST_UINT128_COMPAT=1 LIB_MODE=shared OPT="-DROCKSDB_NAMESPACE=alternative_rocksdb_ns" make V=1 -j32 all check_some | .circleci/cat_ignore_eagain
+      - run: ASSERT_STATUS_CHECKED=1 TEST_UINT128_COMPAT=1 ROCKSDB_MODIFY_NPHASH=1 LIB_MODE=shared OPT="-DROCKSDB_NAMESPACE=alternative_rocksdb_ns" make V=1 -j32 all check_some | .circleci/cat_ignore_eagain
       - post-steps
 
   build-linux-release:
diff --git a/Makefile b/Makefile
index 29c36d61f..37ffa032e 100644
--- a/Makefile
+++ b/Makefile
@@ -414,6 +414,10 @@ ifdef TEST_UINT128_COMPAT
   PLATFORM_CCFLAGS += -DTEST_UINT128_COMPAT=1
   PLATFORM_CXXFLAGS += -DTEST_UINT128_COMPAT=1
 endif
+ifdef ROCKSDB_MODIFY_NPHASH
+  PLATFORM_CCFLAGS += -DROCKSDB_MODIFY_NPHASH=1
+  PLATFORM_CXXFLAGS += -DROCKSDB_MODIFY_NPHASH=1
+endif
 
 # This (the first rule) must depend on "all".
 default: all
diff --git a/db/output_validator.cc b/db/output_validator.cc
index 56b8fe59e..c36c9281e 100644
--- a/db/output_validator.cc
+++ b/db/output_validator.cc
@@ -9,8 +9,8 @@ namespace ROCKSDB_NAMESPACE {
 Status OutputValidator::Add(const Slice& key, const Slice& value) {
   if (enable_hash_) {
     // Generate a rolling 64-bit hash of the key and values
-    paranoid_hash_ = Hash64(key.data(), key.size(), paranoid_hash_);
-    paranoid_hash_ = Hash64(value.data(), value.size(), paranoid_hash_);
+    paranoid_hash_ = NPHash64(key.data(), key.size(), paranoid_hash_);
+    paranoid_hash_ = NPHash64(value.data(), value.size(), paranoid_hash_);
   }
   if (enable_order_check_) {
     TEST_SYNC_POINT_CALLBACK("OutputValidator::Add:order_check",
diff --git a/db/output_validator.h b/db/output_validator.h
index 167b25e06..c2c5f9906 100644
--- a/db/output_validator.h
+++ b/db/output_validator.h
@@ -34,6 +34,8 @@ class OutputValidator {
   }
 
  private:
+  // Not (yet) intended to be persisted, so subject to change
+  // without notice between releases.
   uint64_t GetHash() const { return paranoid_hash_; }
 
   const InternalKeyComparator& icmp_;
diff --git a/env/mock_env.cc b/env/mock_env.cc
index 44c8a01b9..d83e78ffc 100644
--- a/env/mock_env.cc
+++ b/env/mock_env.cc
@@ -16,7 +16,7 @@
 #include "port/sys_time.h"
 #include "rocksdb/file_system.h"
 #include "util/cast_util.h"
-#include "util/murmurhash.h"
+#include "util/hash.h"
 #include "util/random.h"
 #include "util/rate_limiter.h"
 
@@ -32,8 +32,7 @@ class MemFile {
         locked_(false),
         size_(0),
         modified_time_(Now()),
-        rnd_(static_cast<uint32_t>(
-            MurmurHash(fn.data(), static_cast<int>(fn.size()), 0))),
+        rnd_(Lower32of64(GetSliceNPHash64(fn))),
         fsynced_bytes_(0) {}
   // No copying allowed.
   MemFile(const MemFile&) = delete;
diff --git a/util/hash.h b/util/hash.h
index e184eb3e9..539b822f6 100644
--- a/util/hash.h
+++ b/util/hash.h
@@ -36,20 +36,31 @@ extern uint64_t Hash64(const char* data, size_t n, uint64_t seed);
 // Specific optimization without seed (same as seed = 0)
 extern uint64_t Hash64(const char* data, size_t n);
 
-// Non-persistent hash. Must only used for in-memory data structure.
-// The hash results are thus applicable to change. (Thus, it rarely makes
-// sense to specify a seed for this function.)
+// Non-persistent hash. Must only used for in-memory data structures.
+// The hash results are thus subject to change between releases,
+// architectures, build configuration, etc. (Thus, it rarely makes sense
+// to specify a seed for this function, except for a "rolling" hash.)
 // KNOWN FLAW: incrementing seed by 1 might not give sufficiently independent
 // results from previous seed. Recommend incrementing by a large odd number.
-inline uint64_t NPHash64(const char* data, size_t n, uint32_t seed) {
+inline uint64_t NPHash64(const char* data, size_t n, uint64_t seed) {
+#ifdef ROCKSDB_MODIFY_NPHASH
+  // For testing "subject to change"
+  return Hash64(data, n, seed + 123456789);
+#else
   // Currently same as Hash64
   return Hash64(data, n, seed);
+#endif
 }
 
 // Specific optimization without seed (same as seed = 0)
 inline uint64_t NPHash64(const char* data, size_t n) {
+#ifdef ROCKSDB_MODIFY_NPHASH
+  // For testing "subject to change"
+  return Hash64(data, n, 123456789);
+#else
   // Currently same as Hash64
   return Hash64(data, n);
+#endif
 }
 
 // Stable/persistent 32-bit hash. Moderate quality and high speed on
diff --git a/util/hash_test.cc b/util/hash_test.cc
index a6530b686..08fcaf574 100644
--- a/util/hash_test.cc
+++ b/util/hash_test.cc
@@ -585,6 +585,8 @@ TEST(MathTest, CodingGeneric) {
 }
 
 int main(int argc, char** argv) {
+  fprintf(stderr, "NPHash64 id: %x\n",
+          static_cast<int>(ROCKSDB_NAMESPACE::GetSliceNPHash64("RocksDB")));
   ::testing::InitGoogleTest(&argc, argv);
 
   return RUN_ALL_TESTS();