diff --git a/src/hb-common.cc b/src/hb-common.cc
index 8737934de..bfbba6594 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -80,7 +80,7 @@ hb_direction_from_string (const char *str, int len)
   char c = TOLOWER (str[0]);
   for (unsigned int i = 0; i < ARRAY_LENGTH (direction_strings); i++)
     if (c == direction_strings[i][0])
-      return (hb_direction_t) i;
+      return (hb_direction_t) (HB_DIRECTION_LTR + i);
 
   return HB_DIRECTION_INVALID;
 }
@@ -88,8 +88,9 @@ hb_direction_from_string (const char *str, int len)
 const char *
 hb_direction_to_string (hb_direction_t direction)
 {
-  if (likely ((unsigned int) direction < ARRAY_LENGTH (direction_strings)))
-    return direction_strings[direction];
+  if (likely ((unsigned int) (direction - HB_DIRECTION_LTR)
+	      < ARRAY_LENGTH (direction_strings)))
+    return direction_strings[direction - HB_DIRECTION_LTR];
 
   return "invalid";
 }
diff --git a/src/hb-common.h b/src/hb-common.h
index dd86334b9..5d9015d90 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -93,31 +93,31 @@ typedef uint32_t hb_tag_t;
 
 #define HB_TAG_NONE HB_TAG(0,0,0,0)
 
-/* len=-1 means s is NUL-terminated */
-hb_tag_t hb_tag_from_string (const char *s, int len);
+/* len=-1 means str is NUL-terminated */
+hb_tag_t hb_tag_from_string (const char *str, int len);
 
 
 /* hb_direction_t */
 
 typedef enum _hb_direction_t {
-  HB_DIRECTION_INVALID = -1,
-  HB_DIRECTION_LTR = 0,
+  HB_DIRECTION_INVALID = 0,
+  HB_DIRECTION_LTR = 4,
   HB_DIRECTION_RTL,
   HB_DIRECTION_TTB,
   HB_DIRECTION_BTT
 } hb_direction_t;
 
-/* len=-1 means s is NUL-terminated */
+/* len=-1 means str is NUL-terminated */
 hb_direction_t
 hb_direction_from_string (const char *str, int len);
 
 const char *
 hb_direction_to_string (hb_direction_t direction);
 
-#define HB_DIRECTION_IS_HORIZONTAL(dir)	((((unsigned int) (dir)) & ~1U) == 0)
-#define HB_DIRECTION_IS_VERTICAL(dir)	((((unsigned int) (dir)) & ~1U) == 2)
-#define HB_DIRECTION_IS_FORWARD(dir)	((((unsigned int) (dir)) & ~2U) == 0)
-#define HB_DIRECTION_IS_BACKWARD(dir)	((((unsigned int) (dir)) & ~2U) == 1)
+#define HB_DIRECTION_IS_HORIZONTAL(dir)	((((unsigned int) (dir)) & ~1U) == 4)
+#define HB_DIRECTION_IS_VERTICAL(dir)	((((unsigned int) (dir)) & ~1U) == 6)
+#define HB_DIRECTION_IS_FORWARD(dir)	((((unsigned int) (dir)) & ~2U) == 4)
+#define HB_DIRECTION_IS_BACKWARD(dir)	((((unsigned int) (dir)) & ~2U) == 5)
 #define HB_DIRECTION_REVERSE(dir)	((hb_direction_t) (((unsigned int) (dir)) ^ 1))
 
 
@@ -125,7 +125,7 @@ hb_direction_to_string (hb_direction_t direction);
 
 typedef struct _hb_language_t *hb_language_t;
 
-/* len=-1 means s is NUL-terminated */
+/* len=-1 means str is NUL-terminated */
 hb_language_t
 hb_language_from_string (const char *str, int len);
 
diff --git a/test/api/test-common.c b/test/api/test-common.c
index e00e601f9..7441d09db 100644
--- a/test/api/test-common.c
+++ b/test/api/test-common.c
@@ -51,33 +51,38 @@ test_types_int (void)
 static void
 test_types_direction (void)
 {
-  g_assert_cmpint ((signed) HB_DIRECTION_INVALID, ==, -1);
-  g_assert_cmpint (HB_DIRECTION_LTR, ==, 0);
+  g_assert_cmpint ((signed) HB_DIRECTION_INVALID, ==, 0);
+  g_assert_cmpint (HB_DIRECTION_LTR, !=, 0);
 
   g_assert (HB_DIRECTION_IS_HORIZONTAL (HB_DIRECTION_LTR));
   g_assert (HB_DIRECTION_IS_HORIZONTAL (HB_DIRECTION_RTL));
   g_assert (!HB_DIRECTION_IS_HORIZONTAL (HB_DIRECTION_TTB));
   g_assert (!HB_DIRECTION_IS_HORIZONTAL (HB_DIRECTION_BTT));
+  g_assert (!HB_DIRECTION_IS_HORIZONTAL (HB_DIRECTION_INVALID));
 
   g_assert (!HB_DIRECTION_IS_VERTICAL (HB_DIRECTION_LTR));
   g_assert (!HB_DIRECTION_IS_VERTICAL (HB_DIRECTION_RTL));
   g_assert (HB_DIRECTION_IS_VERTICAL (HB_DIRECTION_TTB));
   g_assert (HB_DIRECTION_IS_VERTICAL (HB_DIRECTION_BTT));
+  g_assert (!HB_DIRECTION_IS_VERTICAL (HB_DIRECTION_INVALID));
 
   g_assert (HB_DIRECTION_IS_FORWARD (HB_DIRECTION_LTR));
   g_assert (HB_DIRECTION_IS_FORWARD (HB_DIRECTION_TTB));
   g_assert (!HB_DIRECTION_IS_FORWARD (HB_DIRECTION_RTL));
   g_assert (!HB_DIRECTION_IS_FORWARD (HB_DIRECTION_BTT));
+  g_assert (!HB_DIRECTION_IS_FORWARD (HB_DIRECTION_INVALID));
 
   g_assert (!HB_DIRECTION_IS_BACKWARD (HB_DIRECTION_LTR));
   g_assert (!HB_DIRECTION_IS_BACKWARD (HB_DIRECTION_TTB));
   g_assert (HB_DIRECTION_IS_BACKWARD (HB_DIRECTION_RTL));
   g_assert (HB_DIRECTION_IS_BACKWARD (HB_DIRECTION_BTT));
+  g_assert (!HB_DIRECTION_IS_BACKWARD (HB_DIRECTION_INVALID));
 
   g_assert_cmpint (HB_DIRECTION_REVERSE (HB_DIRECTION_LTR), ==, HB_DIRECTION_RTL);
   g_assert_cmpint (HB_DIRECTION_REVERSE (HB_DIRECTION_RTL), ==, HB_DIRECTION_LTR);
   g_assert_cmpint (HB_DIRECTION_REVERSE (HB_DIRECTION_TTB), ==, HB_DIRECTION_BTT);
   g_assert_cmpint (HB_DIRECTION_REVERSE (HB_DIRECTION_BTT), ==, HB_DIRECTION_TTB);
+  //g_assert_cmpint (HB_DIRECTION_REVERSE (HB_DIRECTION_INVALID), ==, HB_DIRECTION_INVALID);
 
   g_assert_cmpint (HB_DIRECTION_INVALID, ==, hb_direction_from_string (NULL, -1));
   g_assert_cmpint (HB_DIRECTION_INVALID, ==, hb_direction_from_string ("", -1));