diff --git a/src/keypress.h b/src/keypress.h
index 12b743f..6a7220c 100644
--- a/src/keypress.h
+++ b/src/keypress.h
@@ -20,7 +20,8 @@ extern "C"
 		MOD_META = kCGEventFlagMaskCommand,
 		MOD_ALT = kCGEventFlagMaskAlternate,
 		MOD_CONTROL = kCGEventFlagMaskControl,
-		MOD_SHIFT = kCGEventFlagMaskShift
+		MOD_SHIFT = kCGEventFlagMaskShift,
+		MOD_FUNCTION = kCGEventFlagMaskSecondaryFn
 	} MMKeyFlags;
 
 	extern MMKeyFlags flagBuffer;
@@ -32,7 +33,8 @@ extern "C"
 		MOD_META = Mod4Mask,
 		MOD_ALT = Mod1Mask,
 		MOD_CONTROL = ControlMask,
-		MOD_SHIFT = ShiftMask
+		MOD_SHIFT = ShiftMask,
+		MOD_FUNCTION = 0
 	};
 
 	typedef unsigned int MMKeyFlags;
@@ -45,7 +47,8 @@ extern "C"
 		/* MOD_ALT = 0,
 		MOD_CONTROL = 0,
 		MOD_SHIFT = 0, */
-		MOD_META = MOD_WIN
+		MOD_META = MOD_WIN,
+		MOD_FUNCTION = 0
 	};
 
 	typedef unsigned int MMKeyFlags;
diff --git a/src/macos/keypress.c b/src/macos/keypress.c
index 81e5321..6a6e8cf 100644
--- a/src/macos/keypress.c
+++ b/src/macos/keypress.c
@@ -67,6 +67,9 @@ void toggleKeyCode(MMKeyCode code, const bool down, MMKeyFlags flags) {
     if (code == K_SHIFT || code == K_RIGHTSHIFT) {
       flags |= MOD_SHIFT;
     }
+    if (code == K_FUNCTION) {
+      flags |= MOD_FUNCTION;
+    }
 
     MMKeyFlags activeKeyFlags;
     if (down) {
diff --git a/src/main.cc b/src/main.cc
index 71c53a2..c1e6dee 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -365,6 +365,8 @@ int CheckKeyFlags(std::string &flagString, MMKeyFlags *flags) {
         *flags = MOD_CONTROL;
     } else if (flagString == "shift" || flagString == "right_shift") {
         *flags = MOD_SHIFT;
+    } else if (flagString == "fn") {
+        *flags = MOD_FUNCTION;
     } else if (flagString == "none") {
         *flags = MOD_NONE;
     } else {