diff --git a/ChangeLog b/ChangeLog
index 2ec7c88b02..02e0bd76f1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2007-03-18  Matthias Clasen <mclasen@redhat.com> 
+
+	* gtk/gtkentrycompletion.c (gtk_entry_completion_compute_prefix):
+	Ensure that the prefix is valid UTF-8.  (#419568, Nickolay V. Shmyrev)
+
 2007-03-18  Matthias Clasen <mclasen@redhat.com> 
 
 	* modules/input/gtkimcontextmultipress.[hc]:
diff --git a/gtk/gtkentrycompletion.c b/gtk/gtkentrycompletion.c
index d4c51b4f49..d8bc08a06a 100644
--- a/gtk/gtkentrycompletion.c
+++ b/gtk/gtkentrycompletion.c
@@ -1500,7 +1500,7 @@ gtk_entry_completion_compute_prefix (GtkEntryCompletion *completion)
 	  else
 	    {
 	      gchar *p = prefix;
-	      const gchar *q = text;
+	      gchar *q = text;
 	      
 	      while (*p && *p == *q)
 		{
@@ -1509,6 +1509,19 @@ gtk_entry_completion_compute_prefix (GtkEntryCompletion *completion)
 		}
 	      
 	      *p = '\0';
+              
+              if (p > prefix)
+                {
+                  /* strip a partial multibyte character */
+                  q = g_utf8_find_prev_char (prefix, p);
+                  switch (g_utf8_get_char_validated (q, p - q))
+                    {
+                    case (gunichar)-2:
+                    case (gunichar)-1:
+                      *q = 0;
+                    default: ;
+                    }
+                }
 	    }
 	}