diff -ruN panel-plugin.orig/pulseaudio-button.c panel-plugin/pulseaudio-button.c
--- panel-plugin.orig/pulseaudio-button.c	2015-03-18 00:00:00.000000000 +0100
+++ panel-plugin/pulseaudio-button.c	2015-03-18 00:00:00.000000000 +0100
@@ -53,10 +53,10 @@
 
 /* Icons for different volume levels */
 static const char *icons[] = {
-  "audio-volume-muted-symbolic",
-  "audio-volume-low-symbolic",
-  "audio-volume-medium-symbolic",
-  "audio-volume-high-symbolic",
+  "audio-volume-muted",
+  "audio-volume-low",
+  "audio-volume-medium",
+  "audio-volume-high",
   NULL
 };