diff --git a/src/callback.c b/src/callback.c
index a13fd78a..d2d01081 100644
--- a/src/callback.c
+++ b/src/callback.c
@@ -660,9 +660,8 @@ static int waves_callback(int event, int mx, int my, KeySym key, int button, int
                       my_strdup2(1506, &express, ntok);
                     }
                     if(strstr(express, " ")) {
-                      j = xctx->graph_nvars;
                       for(dset = 0 ; dset < xctx->graph_datasets; dset++) {
-                        plot_raw_custom_data(sweep_idx, ofs, ofs + xctx->graph_npoints[dset] - 1, express);
+                        j = plot_raw_custom_data(sweep_idx, ofs, ofs + xctx->graph_npoints[dset] - 1, express);
                         ofs += xctx->graph_npoints[dset];
                       }
                     } else {
diff --git a/src/draw.c b/src/draw.c
index d6989414..485c0421 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -1767,6 +1767,7 @@ static void draw_graph_points(int idx, int first, int last,
   register SPICE_DATA *gv = xctx->graph_values[idx];
 
   dbg(1, "draw_graph_points: idx=%d, first=%d, last=%d, wcnt=%d\n", idx, first, last, wcnt);
+  if(idx == -1) return;
   digital = gr->digital;
   if(digital) {
     s1 = DIG_NWAVES; /* 1/DIG_NWAVES  waveforms fit in graph if unscaled vertically */
@@ -2392,7 +2393,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr)
   char *saven, *savec, *saves, *nptr, *cptr, *sptr;
   const char *ntok, *ctok, *stok;
   char *bus_msb = NULL;
-  int wcnt = 0, idx;
+  int wcnt = 0, idx, expression;
   int measure_p = -1;
   double measure_x;
   double measure_prev_x;
@@ -2439,6 +2440,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr)
       draw_graph_variables(wcnt, wave_color, n_nodes, sweep_idx, flags, ntok, stok, bus_msb, gr);
       /* if ntok following possible 'alias;' definition contains spaces --> custom data plot */
       idx = -1;
+      expression = 0;
       if(xctx->graph_values && !bus_msb) {
         if(strstr(ntok, ";")) {
           my_strdup2(1191, &express, find_nth(ntok, ";", 2));
@@ -2446,11 +2448,11 @@ void draw_graph(int i, const int flags, Graph_ctx *gr)
           my_strdup2(1192, &express, ntok);
         }
         if(strstr(express, " ")) {
-          idx = xctx->graph_nvars;
+          expression = 1;
         }
       }
       /* quickly find index number of ntok variable to be plotted */
-      if( idx == xctx->graph_nvars || (idx = get_raw_index(bus_msb ? bus_msb : express)) != -1 ) {
+      if( expression || (idx = get_raw_index(bus_msb ? bus_msb : express)) != -1 ) {
         int p, dset, ofs;
         int poly_npoints;
         int first, last;
@@ -2499,7 +2501,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr)
                                    sweep_idx, wcnt, n_nodes, gr);
                     }
                   } else {
-                    if(idx == xctx->graph_nvars) plot_raw_custom_data(sweep_idx, first, last, express);
+                    if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express);
                     draw_graph_points(idx, first, last, point, wave_color, wcnt, n_nodes, gr);
                   }
                 }
@@ -2540,7 +2542,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr)
                                sweep_idx, wcnt, n_nodes, gr);
                 }
               } else {
-                if(idx == xctx->graph_nvars) plot_raw_custom_data(sweep_idx, first, last, express);
+                if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express);
                 draw_graph_points(idx, first, last, point, wave_color, wcnt, n_nodes, gr);
               }
             }
diff --git a/src/save.c b/src/save.c
index 29272734..2b018074 100644
--- a/src/save.c
+++ b/src/save.c
@@ -536,7 +536,7 @@ typedef struct {
   double prevx;
 } Stack1;
 
-void plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
+int plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
 {
   int i, p, idx;
   const char *n;
@@ -554,7 +554,7 @@ void plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
     if(stackptr1 >= STACKMAX -2) {
       dbg(0, "stack overflow in graph expression parsing. Interrupted\n");
       my_free(576, &ntok_copy);
-      return;
+      return -1;
     }
     ntok_ptr = NULL;
     dbg(1, "  plot_raw_custom_data(): n = %s\n", n);
@@ -584,7 +584,7 @@ void plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
       if(idx == -1) {
         dbg(1, "plot_raw_custom_data(): no data found: %s\n", n);
         my_free(645, &ntok_copy);
-        return; /* no data found in raw file */
+        return -1; /* no data found in raw file */
       }
       stack1[stackptr1].i = idx;
       stackptr1++;
@@ -716,6 +716,7 @@ void plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
     } /* for(i = 0; i < stackptr1; i++) */
     y[p] = stack2[0];
   }
+  return xctx->graph_nvars;
 }
 
 double get_raw_value(int dataset, int idx, int point)
diff --git a/src/xschem.h b/src/xschem.h
index f1f50c07..6857655f 100644
--- a/src/xschem.h
+++ b/src/xschem.h
@@ -1028,7 +1028,7 @@ extern int get_raw_index(const char *node);
 extern void free_rawfile(int dr);
 extern int read_rawfile(const char *f);
 extern double get_raw_value(int dataset, int idx, int point);
-extern void plot_raw_custom_data(int sweep_idx, int first, int last, const char *ntok);
+extern int plot_raw_custom_data(int sweep_idx, int first, int last, const char *ntok);
 extern int schematic_waves_loaded(void);
 extern int edit_wave_attributes(int what, int i, Graph_ctx *gr);
 extern void draw_graph(int i, int flags, Graph_ctx *gr);