diff --git a/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.cpp b/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.cpp
index 00ec522bf..a45483686 100644
--- a/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.cpp
+++ b/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.cpp
@@ -52,3 +52,10 @@ CodeBlob* JitCodeCache::findRuntimeStub(const void *address) {
   _stubs_lock.unlockShared();
   return stub;
 }
+
+long long JitCodeCache::runtimeStubsMemoryUsage() {
+  _stubs_lock.lockShared();
+  long long usage = _runtime_stubs.memoryUsage();
+  _stubs_lock.unlockShared();
+  return usage;
+}
diff --git a/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.h b/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.h
index 005223384..8d369fe87 100644
--- a/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.h
+++ b/ddprof-lib/src/main/cpp/hotspot/jitCodeCache.h
@@ -38,6 +38,12 @@ class JitCodeCache {
     }
     
     static CodeBlob* findRuntimeStub(const void *address);
+
+    // Approximate heap usage of the runtime-stubs code cache, via
+    // CodeCache::memoryUsage() (a capacity/count-based estimate today; #677
+    // makes it exact). Read under the shared stubs lock because
+    // DynamicCodeGenerated() mutates _runtime_stubs (add()/expand()) concurrently.
+    static long long runtimeStubsMemoryUsage();
     static bool isJitCode(const void* pc) {
         return CodeHeap::contains(pc);
     }
diff --git a/ddprof-lib/src/main/cpp/profiler.cpp b/ddprof-lib/src/main/cpp/profiler.cpp
index 2820ee8c6..07b15a812 100644
--- a/ddprof-lib/src/main/cpp/profiler.cpp
+++ b/ddprof-lib/src/main/cpp/profiler.cpp
@@ -21,6 +21,7 @@
 #include "itimer.h"
 #include "hotspot/vmStructs.inline.h"
 #include "hotspot/hotspotSupport.h"
+#include "hotspot/jitCodeCache.h"
 #include "j9/j9Support.h"
 #include "j9/j9WallClock.h"
 #include "jvmSupport.h"
@@ -1737,8 +1738,11 @@ Error Profiler::dump(const char *path, const int length) {
     const CodeCacheArray& native_libs = _libs->native_libs();
     Counters::set(CODECACHE_NATIVE_COUNT, native_libs.count());
     Counters::set(CODECACHE_NATIVE_SIZE_BYTES, native_libs.memoryUsage());
+    // The runtime-stubs counter reflects the JIT runtime-stubs code cache, a
+    // separate cache from the native libraries (it previously duplicated
+    // native_libs.memoryUsage() by copy-paste). Read under its shared lock.
     Counters::set(CODECACHE_RUNTIME_STUBS_SIZE_BYTES,
-                  native_libs.memoryUsage());
+                  JitCodeCache::runtimeStubsMemoryUsage());
 
     Error err = Error::OK;
     // rotateDictsAndRun rotates the dictionaries, takes lockAll() around the