diff --git a/services/audioflinger/FastMixerDumpState.cpp b/services/audioflinger/FastMixerDumpState.cpp
index 6475f22..2e4fb8c 100644
--- a/services/audioflinger/FastMixerDumpState.cpp
+++ b/services/audioflinger/FastMixerDumpState.cpp
@@ -78,7 +78,12 @@
     uint32_t bounds = mBounds;
     uint32_t newestOpen = bounds & 0xFFFF;
     uint32_t oldestClosed = bounds >> 16;
-    uint32_t n = (newestOpen - oldestClosed) & 0xFFFF;
+
+    //uint32_t n = (newestOpen - oldestClosed) & 0xFFFF;
+    uint32_t n;
+    __builtin_sub_overflow(newestOpen, oldestClosed, &n);
+    n = n & 0xFFFF;
+
     if (n > mSamplingN) {
         ALOGE("too many samples %u", n);
         n = mSamplingN;