diff --git a/cmake/Modules/CompilerRTDarwinUtils.cmake b/cmake/Modules/CompilerRTDarwinUtils.cmake
index e250687..e372da0 100644
--- a/cmake/Modules/CompilerRTDarwinUtils.cmake
+++ b/cmake/Modules/CompilerRTDarwinUtils.cmake
@@ -116,7 +116,7 @@
   if(NOT TEST_COMPILE_ONLY)
     message(STATUS "Finding valid architectures for ${os}...")
     set(SIMPLE_C ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/src.c)
-    file(WRITE ${SIMPLE_C} "#include <stdio.h>\nint main() { printf(__FILE__); return 0; }\n")
+    file(WRITE ${SIMPLE_C} "#include <stdio.h>\nint main(void) { printf(__FILE__); return 0; }\n")
 
     set(os_linker_flags)
     foreach(flag ${DARWIN_${os}_LINK_FLAGS})
diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index da86bdc..f6190ee 100644
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -224,7 +224,7 @@
 # runtime libraries supported by our current compilers cross-compiling
 # abilities.
 set(SIMPLE_SOURCE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/simple.cc)
-file(WRITE ${SIMPLE_SOURCE} "#include <stdlib.h>\n#include <stdio.h>\nint main() { printf(\"hello, world\"); }\n")
+file(WRITE ${SIMPLE_SOURCE} "#include <stdlib.h>\n#include <stdio.h>\nint main(void) { printf(\"hello, world\"); }\n")
 
 # Detect whether the current target platform is 32-bit or 64-bit, and setup
 # the correct commandline flags needed to attempt to target 32-bit and 64-bit.
diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
index fd3d395..42015ef 100644
--- a/lib/builtins/CMakeLists.txt
+++ b/lib/builtins/CMakeLists.txt
@@ -755,7 +755,7 @@
                            SOURCE "#if !(__ARM_FP & 0x8)
                                    #error No double-precision support!
                                    #endif
-                                   int main() { return 0; }")
+                                   int main(void) { return 0; }")
           if(NOT COMPILER_RT_HAS_${arch}_VFP_DP)
             list(REMOVE_ITEM ${arch}_SOURCES ${arm_Thumb1_VFPv2_DP_SOURCES})
           endif()