diff --git a/compiler-rt/lib/fuzzer/FuzzerUtil.h b/compiler-rt/lib/fuzzer/FuzzerUtil.h
--- a/compiler-rt/lib/fuzzer/FuzzerUtil.h
+++ b/compiler-rt/lib/fuzzer/FuzzerUtil.h
@@ -94,7 +94,8 @@
   return static_cast<size_t>((sizeof(unsigned long long) * 8) - Clzll(X) - 1);
 }
 
-inline size_t PageSize() { return 4096; }
+size_t PageSize();
+
 inline uint8_t *RoundUpByPage(uint8_t *P) {
   uintptr_t X = reinterpret_cast<uintptr_t>(P);
   size_t Mask = PageSize() - 1;
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtil.cpp b/compiler-rt/lib/fuzzer/FuzzerUtil.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtil.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtil.cpp
@@ -21,6 +21,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <thread>
+#include <unistd.h>
 
 namespace fuzzer {
 
@@ -234,4 +235,9 @@
   return Res;
 }
 
+size_t PageSize() {
+  static size_t PageSizeCached = sysconf(_SC_PAGESIZE);
+  return PageSizeCached;
+}
+
 }  // namespace fuzzer