diff --git a/src/compton.c b/src/compton.c
index f54e950..fc2f536 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -705,7 +705,8 @@ should_ignore(Display *dpy, unsigned long sequence) {
  * Windows
  */
 
-long determine_evmask(Display *dpy, Window wid, enum win_evmode_t mode) {
+static long
+determine_evmask(Display *dpy, Window wid, win_evmode_t mode) {
   long evmask = NoEventMask;
 
   if (WIN_EVMODE_FRAME == mode || find_win(dpy, wid)) {
diff --git a/src/compton.h b/src/compton.h
index e89728a..2633a98 100644
--- a/src/compton.h
+++ b/src/compton.h
@@ -143,6 +143,12 @@ typedef struct _fade {
   Display *dpy;
 } fade;
 
+typedef enum {
+  WIN_EVMODE_UNKNOWN,
+  WIN_EVMODE_FRAME,
+  WIN_EVMODE_CLIENT
+} win_evmode_t;
+
 extern int root_height, root_width;
 extern Atom atom_client_attr;
 
@@ -356,6 +362,9 @@ set_ignore(Display *dpy, unsigned long sequence);
 static int
 should_ignore(Display *dpy, unsigned long sequence);
 
+static long
+determine_evmask(Display *dpy, Window wid, win_evmode_t mode);
+
 static win *
 find_win(Display *dpy, Window id);