diff --git a/collects/tests/drscheme/drscheme-test-util.ss b/collects/tests/drscheme/drscheme-test-util.ss
index a4956f530c..2de5cf84ba 100644
--- a/collects/tests/drscheme/drscheme-test-util.ss
+++ b/collects/tests/drscheme/drscheme-test-util.ss
@@ -455,6 +455,10 @@
                            
                            ;; return the text of the entire line containing the red text
                            (let ([para (send interactions-text position-paragraph pos)])
+                             (unless (exact-non-negative-integer? para)
+                               (error 'has-error? "got back a bad result from position-paragraph: ~s ~s\n" 
+                                      para
+                                      (list pos (send text last-position))))
                              (send interactions-text get-text
                                    (send interactions-text paragraph-start-position para)
                                    (send interactions-text paragraph-end-position para)))