diff --git a/cmake/flags.cmake b/cmake/flags.cmake
index bc441dd03..97f22f3c1 100644
--- a/cmake/flags.cmake
+++ b/cmake/flags.cmake
@@ -2,6 +2,9 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_CXX_STANDARD 11)
 
+set(CMAKE_C_STANDARD 99)
+set(CMAKE_C_STANDARD_REQUIRED ON)
+
 if ("${CMAKE_BUILD_TYPE}" STREQUAL "")
     set(CMAKE_BUILD_TYPE Release)
 endif()
@@ -13,11 +16,10 @@ endif()
 include(CheckSymbolExists)
 
 if (CMAKE_CXX_COMPILER_ID MATCHES GNU)
-
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wno-strict-aliasing")
     set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -Ofast")
 
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fexceptions -fno-rtti -Wno-class-memaccess")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fexceptions -fno-rtti -Wno-strict-aliasing -Wno-class-memaccess")
     set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Ofast -s")
 
     if (XMRIG_ARMv8)
@@ -46,6 +48,7 @@ if (CMAKE_CXX_COMPILER_ID MATCHES GNU)
     add_definitions(/D_GNU_SOURCE)
 
     if (${CMAKE_VERSION} VERSION_LESS "3.1.0")
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99")
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
     endif()