diff --git a/config/commence.in b/config/commence.in
index 9c8a62300a..af1275cd5d 100644
--- a/config/commence.in
+++ b/config/commence.in
@@ -34,7 +34,7 @@ RUNTEST=$(RUNSERIAL)
 TRACE=:
 
 ## Installation points
-prefix?=@prefix@
+prefix=@prefix@
 exec_prefix=@exec_prefix@
 bindir=@bindir@
 libdir=@libdir@