diff --git a/src/calls-call.c b/src/calls-call.c
index 476a790..cd02242 100644
--- a/src/calls-call.c
+++ b/src/calls-call.c
@@ -340,16 +340,6 @@ calls_call_get_protocol (CallsCall *self)
   return CALLS_CALL_GET_CLASS (self)->get_protocol (self);
 }
 
-static inline gboolean
-tone_key_is_valid (gchar key)
-{
-  return
-       (key >= '0' && key <= '9')
-    || (key >= 'A' && key <= 'D')
-    ||  key == '*'
-    ||  key == '#';
-}
-
 /**
  * calls_call_can_dtmf:
  * @self: a #CallsCall
@@ -379,7 +369,7 @@ calls_call_send_dtmf_tone (CallsCall *self,
                            gchar      key)
 {
   g_return_if_fail (CALLS_IS_CALL (self));
-  g_return_if_fail (tone_key_is_valid (key));
+  g_return_if_fail (dtmf_tone_key_is_valid (key));
 
   CALLS_CALL_GET_CLASS (self)->send_dtmf_tone (self, key);
 }
diff --git a/src/util.c b/src/util.c
index 002065b..fcc1a97 100644
--- a/src/util.c
+++ b/src/util.c
@@ -254,3 +254,22 @@ get_protocol_from_address_with_fallback (const char *target)
 
   return protocol;
 }
+
+/**
+ * dtmf_tone_is_valid:
+ * @key:
+ *
+ * Checks if @key is a valid DTMF keytone
+ *
+ * Returns: %TRUE if @key is 0-9, A-D, * or #, %FALSE otherwise
+ */
+gboolean
+dtmf_tone_key_is_valid (gchar key)
+{
+  return
+    (key >= '0' && key <= '9')
+    || (key >= 'A' && key <= 'D')
+    ||  key == '*'
+    ||  key == '#';
+}
+
diff --git a/src/util.h b/src/util.h
index d94a646..2d38119 100644
--- a/src/util.h
+++ b/src/util.h
@@ -141,6 +141,8 @@ gboolean calls_find_in_store (GListModel *list,
 const char* get_protocol_from_address (const char *target);
 const char* get_protocol_from_address_with_fallback (const char *target);
 
+gboolean dtmf_tone_key_is_valid (char key);
+
 G_END_DECLS
 
 #endif /* CALLS__UTIL_H__ */