diff --git a/configure.ac b/configure.ac
index cfa7208..55eecde 100644
--- a/configure.ac
+++ b/configure.ac
@@ -425,7 +425,7 @@ dnl ############################################################################
 dnl ${prefix} and ${exec_prefix} are undefined here if --prefix is not used in command line
 dnl Let define ${prefix} and ${exec_prefix}
 test "x$prefix" = "xNONE" && prefix=$ac_default_prefix
-test "x$exec_prefix" = "xNONE" && exec_prefix='${prefix}'
+test "x$exec_prefix" = "xNONE" && exec_prefix=${prefix}
 
 if test x${libexecdir} = x'${exec_prefix}/libexec'; then
     EXTHELPERSDIR=${prefix}/libexec/${PACKAGE}/ext.d