diff --git a/Shorewall/Perl/Shorewall/Nat.pm b/Shorewall/Perl/Shorewall/Nat.pm
index 924e80ff8..b918b0479 100644
--- a/Shorewall/Perl/Shorewall/Nat.pm
+++ b/Shorewall/Perl/Shorewall/Nat.pm
@@ -29,7 +29,7 @@ use Shorewall::Config qw(:DEFAULT :internal);
 use Shorewall::IPAddrs;
 use Shorewall::Zones;
 use Shorewall::Chains qw(:DEFAULT :internal);
-use Shorewall::Providers qw( lookup_provider );
+use Shorewall::Providers qw( provider_realm );
 
 use strict;
 
@@ -144,7 +144,7 @@ sub process_one_masq1( $$$$$$$$$$ )
 	    fatal_error "Missing Provider ($fullinterface)" unless supplied $provider;
 
 	    $fullinterface =~ s/[(]\w*[)]//;
-	    my $realm = lookup_provider( $provider );
+	    my $realm = provider_realm( $provider );
 
 	    fatal_error "$provider is not a shared-interface provider" unless $realm;
 
diff --git a/Shorewall/Perl/Shorewall/Providers.pm b/Shorewall/Perl/Shorewall/Providers.pm
index f526eefe8..daf411084 100644
--- a/Shorewall/Perl/Shorewall/Providers.pm
+++ b/Shorewall/Perl/Shorewall/Providers.pm
@@ -43,7 +43,7 @@ our @EXPORT = qw( process_providers
 		  setup_load_distribution
 		  have_providers
 	       );
-our @EXPORT_OK = qw( initialize lookup_provider );
+our @EXPORT_OK = qw( initialize provider_realm );
 our $VERSION = '4.4_24';
 
 use constant { LOCAL_TABLE   => 255,
@@ -377,6 +377,26 @@ sub start_provider( $$$$ ) {
     }
 }
 
+#
+# Look up a provider and return it's number. If unknown provider, 0 is returned
+#
+sub lookup_provider( $ ) {
+    my $provider    = $_[0];
+    my $providerref = $providers{ $provider };
+
+    unless ( $providerref ) {
+	my $provider_number = numeric_value $provider;
+
+	if ( defined $provider_number ) {
+	    for ( values %providers ) {
+		$providerref = $_, last if $_->{number} == $provider_number;
+	    }
+	}
+    }
+
+    $providerref ? $providerref->{number} : 0;
+}
+
 #
 # Process a record in the providers file
 #
@@ -572,6 +592,8 @@ sub process_a_provider( $ ) {
 
     if ( $duplicate ne '-' ) {
 	fatal_error "The DUPLICATE column must be empty when USE_DEFAULT_RT=Yes" if $config{USE_DEFAULT_RT};
+	my $p = lookup_provider( $duplicate );
+	warning_message "Unknown routing table ($duplicate)" unless $p && ( $p == MAIN_TABLE || $p < BALANCE_TABLE );
     } elsif ( $copy ne '-' ) {
 	fatal_error "The COPY column must be empty when USE_DEFAULT_RT=Yes" if $config{USE_DEFAULT_RT};
 	fatal_error 'A non-empty COPY column requires that a routing table be specified in the DUPLICATE column' unless $copy eq 'none';
@@ -1717,7 +1739,11 @@ sub compile_updown() {
 	);
 }
 
-sub lookup_provider( $ ) {
+#
+# Lookup the passed provider. Raise a fatal error if provider is unknown. 
+# Return the provider's realm if it is a shared provider; otherwise, return zero
+#
+sub provider_realm( $ ) {
     my $provider    = $_[0];
     my $providerref = $providers{ $provider };