diff --git a/include/grpc/support/port_platform.h b/include/grpc/support/port_platform.h
index 864d669eda0..671648a976b 100644
--- a/include/grpc/support/port_platform.h
+++ b/include/grpc/support/port_platform.h
@@ -136,11 +136,12 @@
 #endif
 #if TARGET_OS_IPHONE
 #define GPR_CPU_IPHONE 1
+#define GPR_PTHREAD_TLS 1
 #else /* TARGET_OS_IPHONE */
 #define GPR_CPU_POSIX 1
+#define GPR_GCC_TLS 1
 #endif
 #define GPR_GCC_ATOMIC 1
-#define GPR_GCC_TLS 1
 #define GPR_POSIX_LOG 1
 #define GPR_POSIX_MULTIPOLL_WITH_POLL 1
 #define GPR_POSIX_WAKEUP_FD 1