--- a/src/functions.c
+++ b/src/functions.c
@@ -65,7 +65,7 @@
 # endif
 #endif
 
-DEFSYM(root, "root");
+extern DEFSYM(root, "root");
 DEFSYM(after_restacking_hook, "after-restacking-hook");
 DEFSYM(position, "position");
 DEFSYM(spacing, "spacing");
--- a/src/flippers.c
+++ b/src/flippers.c
@@ -22,10 +22,10 @@
 
 static Window edge_left, edge_right, edge_top, edge_bottom;
 
-DEFSYM(left, "left");
-DEFSYM(right, "right");
-DEFSYM(top, "top");
-DEFSYM(bottom, "bottom");
+extern DEFSYM(left, "left");
+extern DEFSYM(right, "right");
+extern DEFSYM(top, "top");
+extern DEFSYM(bottom, "bottom");
 DEFSYM(enter_flipper_hook, "enter-flipper-hook");
 DEFSYM(leave_flipper_hook, "leave-flipper-hook");
 
--- a/src/windows.c
+++ b/src/windows.c
@@ -75,7 +75,7 @@
 DEFSYM(north, "north");
 DEFSYM(north_east, "north-east");
 DEFSYM(west, "west");
-DEFSYM(center, "center");
+extern DEFSYM(center, "center");
 DEFSYM(east, "east");
 DEFSYM(south_west, "south-west");
 DEFSYM(south, "south");