diff --git a/mosquitto.spec b/mosquitto.spec
index aebff1c..5cb43da 100644
--- a/mosquitto.spec
+++ b/mosquitto.spec
@@ -38,7 +38,7 @@ Development headers and libraries for %{name}
 %prep
 %setup -q
 # Set the install prefix to /usr
-sed -i "s|prefix=/usr/local|prefix=/usr|" config.mk
+sed -i "s|prefix?=/usr/local|prefix?=/usr|" config.mk
 # Don't strip binaries on install: rpmbuild will take care of it
 sed -i "s|(INSTALL) -s|(INSTALL)|g" lib/Makefile src/Makefile client/Makefile