diff --git a/firmware/common/scripts/prompt.py b/firmware/common/scripts/prompt.py
index 07c847f5..89217af9 100644
--- a/firmware/common/scripts/prompt.py
+++ b/firmware/common/scripts/prompt.py
@@ -27,7 +27,7 @@
 print("//\n//\tThis file is automatically generated\n//")
 print("#define PROMPT \"Morpheus Firmware: {0}\\r\"".format(version))
 
-m = re.match("^v(\\d+)\\.(\\d+)\\.(\\d+).*$",plainVersion+".0")
+m = re.match("^v(\\d+)\\.(\\d+)\\.(\\d+).*$",plainVersion.replace("-",".")+".0")
 assert m is not None,"Cannot parse version string "+plainVersion
 
 print("#define VERSION_MAJOR ({0})".format(m.group(1)))