diff --git a/src/frontend/inp.c b/src/frontend/inp.c
index aca467a86..21a5dc86a 100644
--- a/src/frontend/inp.c
+++ b/src/frontend/inp.c
@@ -890,23 +890,35 @@ inp_spsource(FILE *fp, bool comfile, char *filename, bool intfile)
             /* handle .if ... .elseif ... .else ... .endif statements. */
             dotifeval(deck);
 
+            /* get csparams and create vectors, available
+               in plot 'const' of a .control section */
             for (dd = deck; dd; dd = dd->nextcard) {
-                /* get csparams and create vectors, being
-                   available in .control section, in plot 'const' */
                 if (ciprefix(".csparam", dd->line)) {
                     wordlist *wlist = NULL;
                     char *cstoken[3];
                     int i;
                     dd->line[0] = '*';
                     s = skip_ws(dd->line + 8);
-                    cstoken[0] = gettok_char(&s, '=', FALSE, FALSE);
-                    cstoken[1] = gettok_char(&s, '=', TRUE, FALSE);
-                    cstoken[2] = gettok(&s);
-                    for (i = 3; --i >= 0; ) {
-                        wlist = wl_cons(cstoken[i], wlist);
+                    while (s && *s) {
+                        cstoken[0] = gettok_char(&s, '=', FALSE, FALSE);
+                        cstoken[1] = gettok_char(&s, '=', TRUE, FALSE);
+                        cstoken[2] = gettok(&s);
+                        /* guard against buggy input line */
+                        if (!cstoken[0] || !cstoken[1] || !cstoken[2] || strchr(cstoken[2],'=')) {
+                            tfree(cstoken[0]);
+                            tfree(cstoken[1]);
+                            tfree(cstoken[2]);
+                            fprintf(stderr, "Warning: bad csparam definition, skipped!\n");
+                            fprintf(stderr, "    in line %d, .%s\n\n", dd->linenum, dd->line + 1);
+                            continue;
+                        }
+                        for (i = 3; --i >= 0; ) {
+                            wlist = wl_cons(cstoken[i], wlist);
+                        }
+                        com_let(wlist);
+                        wl_free(wlist);
+                        wlist = NULL;
                     }
-                    com_let(wlist);
-                    wl_free(wlist);
                 }
             }