diff --git a/libraries/adlmidi/CMakeLists.txt b/libraries/adlmidi/CMakeLists.txt
index c80d4213f..045d26e66 100644
--- a/libraries/adlmidi/CMakeLists.txt
+++ b/libraries/adlmidi/CMakeLists.txt
@@ -8,7 +8,7 @@ if( ZD_CMAKE_COMPILER_IS_GNUC_COMPATIBLE )
 	set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wno-unused-parameter -fomit-frame-pointer" )
 endif()
 
-set (CMAKE_C_FLAGS ${CMAKE_C_FLAGS} ${ZD_FASTMATH_FLAG})
+set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${ZD_FASTMATH_FLAG}")
 
 add_library( adl STATIC
 	adldata.cpp
diff --git a/libraries/opnmidi/CMakeLists.txt b/libraries/opnmidi/CMakeLists.txt
index d9101922d..d6a469f11 100644
--- a/libraries/opnmidi/CMakeLists.txt
+++ b/libraries/opnmidi/CMakeLists.txt
@@ -12,7 +12,7 @@ if( ZD_CMAKE_COMPILER_IS_GNUC_COMPATIBLE )
 	set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wno-unused-parameter -fomit-frame-pointer" )
 endif()
 
-set (CMAKE_C_FLAGS ${CMAKE_C_FLAGS} ${ZD_FASTMATH_FLAG})
+set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${ZD_FASTMATH_FLAG}")
 
 add_library( opn STATIC
 	chips/gens_opn2.cpp