diff --git a/config/aclocal.m4 b/config/aclocal.m4
index b36eb03c..b3a83380 100644
--- a/config/aclocal.m4
+++ b/config/aclocal.m4
@@ -4799,7 +4799,7 @@ AC_CACHE_CHECK([whether $FPP fulfils requested features],
 
   ac_cv_fpp_build_rule=indirect
 
-if test ac_fpp_ok == no; then
+if test ac_fpp_ok = no; then
   AC_MSG_ERROR([Cannot find a Fortran preprocessor with the requested features])
 fi
 
diff --git a/config/m4/fortran.m4 b/config/m4/fortran.m4
index 441ee239..904d70f0 100644
--- a/config/m4/fortran.m4
+++ b/config/m4/fortran.m4
@@ -3107,7 +3107,7 @@ AC_CACHE_CHECK([whether $FPP fulfils requested features],
 
   ac_cv_fpp_build_rule=indirect
 
-if test ac_fpp_ok == no; then
+if test ac_fpp_ok = no; then
   AC_MSG_ERROR([Cannot find a Fortran preprocessor with the requested features])
 fi
 
diff --git a/configure b/configure
index 19261327..4269c3e9 100755
--- a/configure
+++ b/configure
@@ -4781,7 +4781,7 @@ echo "${ECHO_T}$ac_cv_prog_fpp_ok" >&6; }
 
   ac_cv_fpp_build_rule=indirect
 
-if test ac_fpp_ok == no; then
+if test ac_fpp_ok = no; then
   { { echo "$as_me:$LINENO: error: Cannot find a Fortran preprocessor with the requested features" >&5
 echo "$as_me: error: Cannot find a Fortran preprocessor with the requested features" >&2;}
    { (exit 1); exit 1; }; }