diff --git a/src/idna.c b/src/idna.c
index 93d982ca018f2d39d9c0ffab07998c2c637029eb..858b19d00ee4239879357f2ec0231cb6d84e4186 100644
--- a/src/idna.c
+++ b/src/idna.c
@@ -274,6 +274,9 @@ long uv__idna_toascii(const char* s, const char* se, char* d, char* de) {
   char* ds;
   int rc;
 
+  if (s == se)
+    return UV_EINVAL;
+
   ds = d;
 
   si = s;
@@ -308,8 +311,9 @@ long uv__idna_toascii(const char* s, const char* se, char* d, char* de) {
       return rc;
   }
 
-  if (d < de)
-    *d++ = '\0';
+  if (d >= de)
+    return UV_EINVAL;
 
+  *d++ = '\0';
   return d - ds;  /* Number of bytes written. */
 }
diff --git a/test/test-idna.c b/test/test-idna.c
index 77af3a9da0341c53c05a06920dd909324c00d8d9..180a6a685ac23f3183d84ab8d77b43c26f341e40 100644
--- a/test/test-idna.c
+++ b/test/test-idna.c
@@ -99,7 +99,7 @@ TEST_IMPL(utf8_decode1) {
 TEST_IMPL(utf8_decode1_overrun) {
   const char* p;
   char b[1];
-
+  char c[1];
   /* Single byte. */
   p = b;
   b[0] = 0x7F;
@@ -110,7 +110,11 @@ TEST_IMPL(utf8_decode1_overrun) {
   p = b;
   b[0] = 0xC0;
   ASSERT_EQ((unsigned int) -1, uv__utf8_decode1(&p, b + 1));
-  ASSERT_EQ(p, b + 1);
+  ASSERT_PTR_EQ(p, b + 1);
+
+  b[0] = 0x7F;
+  ASSERT_EQ(UV_EINVAL, uv__idna_toascii(b, b + 0, c, c + 1));
+  ASSERT_EQ(UV_EINVAL, uv__idna_toascii(b, b + 1, c, c + 1));
 
   return 0;
 }
@@ -145,8 +149,8 @@ TEST_IMPL(idna_toascii) {
   /* Illegal inputs. */
   F("\xC0\x80\xC1\x80", UV_EINVAL);  /* Overlong UTF-8 sequence. */
   F("\xC0\x80\xC1\x80.com", UV_EINVAL);  /* Overlong UTF-8 sequence. */
+  F("", UV_EINVAL);
   /* No conversion. */
-  T("", "");
   T(".", ".");
   T(".com", ".com");
   T("example", "example");