diff --git a/config/auto/icu.pm b/config/auto/icu.pm
index f78ec8681a..b31857558a 100644
--- a/config/auto/icu.pm
+++ b/config/auto/icu.pm
@@ -388,14 +388,7 @@ sub _handle_ccflags_status {
     else {
         my $icuheaders = $arg->{icuheaders};
 
-        my $icuflags;
-        if ($icuheaders =~ /\s/) {
-            $icuflags = "-I \"$arg->{icuheaders}\"";
-        }
-        else {
-            $icuflags = "-I $arg->{icuheaders}";
-        }
-
+        my $icuflags = qq{-isystem "$icuheaders"};
         $conf->debug( "Adding $icuflags to ccflags for icu headers.\n");
         $conf->data->add( ' ', ccflags => $icuflags );
     }
diff --git a/config/auto/warnings.pm b/config/auto/warnings.pm
index 4a8857f4d4..d9881decc7 100644
--- a/config/auto/warnings.pm
+++ b/config/auto/warnings.pm
@@ -161,7 +161,7 @@ sub _init {
         -Wmissing-prototypes
         -Werror=nested-externs
         -Werror=old-style-definition
-        -Wstrict-prototypes
+        -Werror=strict-prototypes
     );
 
     $gcc->{'basic'} = [ @gcc_or_gpp_basic, @gcc_basic ];