diff --git a/classes/externalgitsrc.bbclass b/classes/externalgitsrc.bbclass
index 04ec9d7..4b6ede9 100644
--- a/classes/externalgitsrc.bbclass
+++ b/classes/externalgitsrc.bbclass
@@ -1,7 +1,6 @@
 # Provides git describe tag from yocto root directory
 
 EXTERNALSRC = "${@os.path.abspath(os.path.join("${TOPDIR}", os.pardir))}"
-EXTERNALSRC_GIT_SRCREV = "${@get_externalsrc_rev(d)}"
 
 def get_externalsrc_rev(d):
     import subprocess
@@ -14,3 +13,4 @@ def get_externalsrc_rev(d):
     d.setVar('BB_DONT_CACHE', '1')
     return rev
 
+EXTERNALSRC_GIT_SRCREV := "${@get_externalsrc_rev(d)}"