diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_solaris.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_solaris.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_solaris.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_solaris.cpp
@@ -76,10 +76,16 @@
 
 // Illumos' declaration of madvise cannot be made visible if _XOPEN_SOURCE
 // is defined as g++ does on Solaris.
-extern "C" int madvise(caddr_t, size_t, int);
+//
+// This declaration is consistent with Solaris 11.4. Both Illumos and Solaris
+// versions older than 11.4 declared madvise with a caddr_t as the first
+// argument, but we don't currently support Solaris versions older than 11.4,
+// and as mentioned above the declaration is not visible on Illumos so we can
+// use any declaration we like on Illumos.
+extern "C" int madvise(void *, size_t, int);
 
 int internal_madvise(uptr addr, uptr length, int advice) {
-  return madvise((caddr_t)addr, length, advice);
+  return madvise((void *)addr, length, advice);
 }
 
 DECLARE__REAL_AND_INTERNAL(uptr, close, fd_t fd) {