1 files changed, 12 insertions, 4 deletions
diff --git a/io.c b/io.c
index ea550592bb..a3a45c0b12 100644
--- a/io.c
+++ b/io.c
@@ -4786,11 +4786,19 @@ extract_binmode(VALUE opthash, int *fmode)
     if (!NIL_P(opthash)) {
 	VALUE v;
 	v = rb_hash_aref(opthash, sym_textmode);
-	if (!NIL_P(v) && RTEST(v))
-            *fmode |= FMODE_TEXTMODE;
+	if (!NIL_P(v)) {
+	    if (*fmode & FMODE_TEXTMODE)
+		rb_raise(rb_eArgError, "textmode specified twice");
+	    if (RTEST(v))
+		*fmode |= FMODE_TEXTMODE;
+	}
 	v = rb_hash_aref(opthash, sym_binmode);
-	if (!NIL_P(v) && RTEST(v))
-            *fmode |= FMODE_BINMODE;
+	if (!NIL_P(v)) {
+	    if (*fmode & FMODE_BINMODE)
+		rb_raise(rb_eArgError, "binmode specified twice");
+	    if (RTEST(v))
+		*fmode |= FMODE_BINMODE;
+	}
 
 	if ((*fmode & FMODE_BINMODE) && (*fmode & FMODE_TEXTMODE))
 	    rb_raise(rb_eArgError, "both textmode and binmode specified");