diff --git a/compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp b/compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
--- a/compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
+++ b/compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
@@ -99,6 +99,7 @@
   else
     AdjustedSampleRatePlusOne = 2;
 
+  initPRNG();
   ThreadLocals.NextSampleCounter =
       (getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1;
 
diff --git a/compiler-rt/lib/gwp_asan/random.h b/compiler-rt/lib/gwp_asan/random.h
--- a/compiler-rt/lib/gwp_asan/random.h
+++ b/compiler-rt/lib/gwp_asan/random.h
@@ -12,6 +12,9 @@
 #include <stdint.h>
 
 namespace gwp_asan {
+// Initialise the PRNG, using time and thread ID as the seed.
+void initPRNG();
+
 // xorshift (32-bit output), extremely fast PRNG that uses arithmetic operations
 // only. Seeded using walltime.
 uint32_t getRandomUnsigned32();
diff --git a/compiler-rt/lib/gwp_asan/random.cpp b/compiler-rt/lib/gwp_asan/random.cpp
--- a/compiler-rt/lib/gwp_asan/random.cpp
+++ b/compiler-rt/lib/gwp_asan/random.cpp
@@ -11,9 +11,18 @@
 
 #include <time.h>
 
+// Initialised to a magic constant so that an uninitialised GWP-ASan won't
+// regenerate its sample counter for as long as possible. The xorshift32()
+// algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
+// 0xfffffea4.
+GWP_ASAN_TLS_INITIAL_EXEC uint32_t RandomState = 0xff82eb50;
+
 namespace gwp_asan {
+void initPRNG() {
+  RandomState = time(nullptr) + getThreadID();
+}
+
 uint32_t getRandomUnsigned32() {
-  thread_local uint32_t RandomState = time(nullptr) + getThreadID();
   RandomState ^= RandomState << 13;
   RandomState ^= RandomState >> 17;
   RandomState ^= RandomState << 5;