diff --git a/src/frontend/plotting/grid.c b/src/frontend/plotting/grid.c
index c7e5c0710..41dccfd24 100644
--- a/src/frontend/plotting/grid.c
+++ b/src/frontend/plotting/grid.c
@@ -16,7 +16,6 @@ Modified: 2001 AlansFixes
 #include "../display.h"
 
 #define RAD_TO_DEG      (180.0 / M_PI)
-#define LABEL_CHARS     16
 
 typedef enum { x_axis, y_axis } Axis;
 
@@ -230,7 +229,7 @@ lingrid(GRAPH *graph, double lo, double hi, double delta, int type, Axis axis)
     int max;
     static double dd[2];
     int mult = 1;
-    char buf[LABEL_CHARS], *s;
+    char buf[GRAPH_UNITS_LENGTH], *s;
     int slim, digits;
 
     if (axis == y_axis && graph->grid.ysized) {
@@ -495,7 +494,7 @@ drawlingrid(GRAPH *graph, char *units, int spacing, int nsp, double dst, double
 {
     int i, j;
     double m, step;
-    char buf[LABEL_CHARS];
+    char buf[GRAPH_UNITS_LENGTH];
 
     NG_IGNORE(onedec);
     NG_IGNORE(mult);
@@ -563,7 +562,7 @@ loggrid(GRAPH *graph, double lo, double hi, int type, Axis axis)
     int i, j;
     double k;
     double decs;
-    char buf[LABEL_CHARS], *s;
+    char buf[GRAPH_UNITS_LENGTH], *s;
 
     if (axis == x_axis && graph->grid.xsized) {
         lmt = graph->grid.xaxis.log.lmt;
@@ -663,7 +662,7 @@ drawloggrid(GRAPH *graph, char *units, int hmt, int lmt, int decsp, int subs, in
 {
     int i, j, k, m;
     double t;
-    char buf[LABEL_CHARS];
+    char buf[GRAPH_UNITS_LENGTH];
 
     /* Now plot every pp'th decade line, with subs lines between them. */
     if (subs > 1)
diff --git a/src/include/ngspice/graph.h b/src/include/ngspice/graph.h
index a4e0059a7..dbca872d8 100644
--- a/src/include/ngspice/graph.h
+++ b/src/include/ngspice/graph.h
@@ -17,6 +17,7 @@ Author: 1988 Jeffrey M. Hsu
 
 struct _keyed;
 
+#define GRAPH_UNITS_LENGTH  16
 
 /* Device-independent data structure for plots. */
 
@@ -68,7 +69,7 @@ struct graph {
       int circular;         /* TRUE if circular plot area */
       union {
         struct {
-                char units[16];     /* unit labels */
+                char units[GRAPH_UNITS_LENGTH];  /* unit labels */
                 int     spacing, numspace;
                 double  distance, lowlimit, highlimit;
                 int     mult;
@@ -79,11 +80,11 @@ struct graph {
                 int     digits;
         } lin;
         struct {
-                char units[16];     /* unit labels */
+                char units[GRAPH_UNITS_LENGTH];  /* unit labels */
                 int hmt, lmt, decsp, subs, pp;
         } log;
         struct {
-                char units[16];     /* unit labels */
+                char units[GRAPH_UNITS_LENGTH];  /* unit labels */
                 int radius, center;
                 double mrad;
                 int lmt;