diff --git a/pcbnew/drc/drc_test_provider_diff_pair_coupling.cpp b/pcbnew/drc/drc_test_provider_diff_pair_coupling.cpp
index 7be28e9f8e..24d7dd848b 100644
--- a/pcbnew/drc/drc_test_provider_diff_pair_coupling.cpp
+++ b/pcbnew/drc/drc_test_provider_diff_pair_coupling.cpp
@@ -150,7 +150,7 @@ static int matchDpSuffix( const wxString& aNetName, wxString& aComplementNet,
 }
 
 
-static int isNetADiffPair( BOARD* aBoard, int aNet, int& aNetP, int& aNetN )
+int DRC_ENGINE::IsNetADiffPair( BOARD* aBoard, int aNet, int& aNetP, int& aNetN )
 {
     wxString refName = aBoard->FindNet( aNet )->GetNetname();
     wxString dummy, coupledNetName;
@@ -370,7 +370,7 @@ bool test::DRC_TEST_PROVIDER_DIFF_PAIR_COUPLING::Run()
                 auto citem = static_cast<BOARD_CONNECTED_ITEM*>( item );
                 int refNet = citem->GetNetCode();
 
-                if( !isNetADiffPair( m_board, refNet, key.netP, key.netN ) ) // not our business
+                if( !DRC_ENGINE::IsNetADiffPair( m_board, refNet, key.netP, key.netN ) ) // not our business
                     return true;
 
                 drc_dbg(10, "eval dp %p\n", item );
diff --git a/pcbnew/pcb_expr_evaluator.cpp b/pcbnew/pcb_expr_evaluator.cpp
index 5ade2a29b6..3d2354835b 100644
--- a/pcbnew/pcb_expr_evaluator.cpp
+++ b/pcbnew/pcb_expr_evaluator.cpp
@@ -34,6 +34,7 @@
 #include <connectivity/connectivity_algo.h>
 #include <connectivity/from_to_cache.h>
 
+#include <drc/drc_engine.h>
 
 
 bool exprFromTo( LIBEVAL::CONTEXT* aCtx, void* self )
@@ -59,20 +60,12 @@ bool exprFromTo( LIBEVAL::CONTEXT* aCtx, void* self )
         return true;
     }
 
-    int r =0 ;
-
     if( ftCache->IsOnFromToPath( static_cast<BOARD_CONNECTED_ITEM*>( item ),
         argFrom->AsString(), argTo->AsString() ) )
     {
         result->Set(1.0);
-        r = 1;
-
     }
 
-    /*printf("isonfromto %p %s %s -> %d\n", static_cast<BOARD_CONNECTED_ITEM*>( item ),
-        (const char *)argFrom->AsString(),
-        (const char *)argTo->AsString(), r );*/
-
     return true;
 }
 
@@ -330,9 +323,29 @@ static void isBlindBuriedVia( LIBEVAL::CONTEXT* aCtx, void* self )
     {
         result->Set ( 1.0 );
     }
-
 }
 
+
+static void isDiffPair( LIBEVAL::CONTEXT* aCtx, void* self )
+{
+    PCB_EXPR_VAR_REF* vref = static_cast<PCB_EXPR_VAR_REF*>( self );
+    BOARD_ITEM*       item = vref ? vref->GetObject( aCtx ) : nullptr;
+    LIBEVAL::VALUE*   result = aCtx->AllocValue();
+
+    result->Set( 0.0 );
+    aCtx->Push( result );
+
+    if( item->IsConnected() )
+    {
+        int net = static_cast<BOARD_CONNECTED_ITEM*>( item )->GetNetCode();
+        int net_p, net_n;
+
+        if( DRC_ENGINE::IsNetADiffPair( item->GetBoard(), net, net_p, net_n ) )
+            result->Set( 1.0 );
+    }
+}
+
+
 PCB_EXPR_BUILTIN_FUNCTIONS::PCB_EXPR_BUILTIN_FUNCTIONS()
 {
     RegisterAllFunctions();
@@ -350,7 +363,7 @@ void PCB_EXPR_BUILTIN_FUNCTIONS::RegisterAllFunctions()
     RegisterFunc( "isBlindBuriedVia()", isBlindBuriedVia );
     RegisterFunc( "memberOf('x')", memberOf );
     RegisterFunc( "fromTo('x','y')", exprFromTo );
-    //RegisterFunc( "isDiffPair()", exprFromTo );
+    RegisterFunc( "isDiffPair()", isDiffPair );
 }