diff --git a/PIL/Jpeg2KImagePlugin.py b/PIL/Jpeg2KImagePlugin.py
index f57f4a784..048fe2af1 100644
--- a/PIL/Jpeg2KImagePlugin.py
+++ b/PIL/Jpeg2KImagePlugin.py
@@ -76,6 +76,7 @@ def _parse_jp2_header(fp):
 
     size = None
     mode = None
+    bpc = None
     
     hio = io.BytesIO(header)
     while True:
@@ -93,7 +94,9 @@ def _parse_jp2_header(fp):
               = struct.unpack('>IIHBBBB', content)
             size = (width, height)
             if unkc:
-                if nc == 1:
+                if nc == 1 and bpc == 15:
+                    mode = 'I'
+                elif nc == 1:
                     mode = 'L'
                 elif nc == 2:
                     mode = 'LA'
@@ -113,7 +116,9 @@ def _parse_jp2_header(fp):
                         mode = 'RGBA'
                     break
                 elif cs == 17: # grayscale
-                    if nc == 1:
+                    if nc == 1 and bpc == 15:
+                        mode = 'I'
+                    elif nc == 1:
                         mode = 'L'
                     elif nc == 2:
                         mode = 'LA'
@@ -122,7 +127,7 @@ def _parse_jp2_header(fp):
                     if nc == 3:
                         mode = 'RGB'
                     elif nc == 4:
-                        mode == 'RGBA'
+                        mode = 'RGBA'
                     break
 
     return (size, mode)
diff --git a/libImaging/Jpeg2KDecode.c b/libImaging/Jpeg2KDecode.c
index 6b6176c78..89ad10136 100644
--- a/libImaging/Jpeg2KDecode.c
+++ b/libImaging/Jpeg2KDecode.c
@@ -135,6 +135,56 @@ j2ku_gray_l(opj_image_t *in, const JPEG2KTILEINFO *tileinfo,
     }
 }
 
+
+static void
+j2ku_gray_i(opj_image_t *in, const JPEG2KTILEINFO *tileinfo,
+            const UINT8 *tiledata, Imaging im)
+{
+    unsigned x0 = tileinfo->x0 - in->x0, y0 = tileinfo->y0 - in->y0;
+    unsigned w = tileinfo->x1 - tileinfo->x0;
+    unsigned h = tileinfo->y1 - tileinfo->y0;
+
+    int shift = 16 - in->comps[0].prec;
+    int offset = in->comps[0].sgnd ? 1 << (in->comps[0].prec - 1) : 0;
+    int csiz = (in->comps[0].prec + 7) >> 3;
+
+    unsigned x, y;
+
+    if (csiz == 3)
+        csiz = 4;
+
+    if (shift < 0)
+        offset += 1 << (-shift - 1);
+
+    switch (csiz) {
+    case 1:
+        for (y = 0; y < h; ++y) {
+            const UINT8 *data = &tiledata[y * w];
+            UINT32 *row = (UINT32 *)im->image[y0 + y] + x0;
+            for (x = 0; x < w; ++x)
+                *row++ = j2ku_shift(offset + *data++, shift);
+        }
+        break;
+    case 2:
+        for (y = 0; y < h; ++y) {
+            const UINT16 *data = (const UINT16 *)&tiledata[2 * y * w];
+            UINT32 *row = (UINT32 *)im->image[y0 + y] + x0;
+            for (x = 0; x < w; ++x)
+                *row++ = j2ku_shift(offset + *data++, shift);
+        }
+        break;
+    case 4:
+        for (y = 0; y < h; ++y) {
+            const UINT32 *data = (const UINT32 *)&tiledata[4 * y * w];
+            UINT32 *row = (UINT32 *)im->image[y0 + y] + x0;
+            for (x = 0; x < w; ++x)
+                *row++ = j2ku_shift(offset + *data++, shift);
+        }
+        break;
+    }
+}
+
+
 static void
 j2ku_gray_rgb(opj_image_t *in, const JPEG2KTILEINFO *tileinfo,
               const UINT8 *tiledata, Imaging im)
@@ -466,6 +516,7 @@ j2ku_sycca_rgba(opj_image_t *in, const JPEG2KTILEINFO *tileinfo,
 
 static const struct j2k_decode_unpacker j2k_unpackers[] = {
     { "L", OPJ_CLRSPC_GRAY, 1, j2ku_gray_l },
+    { "I", OPJ_CLRSPC_GRAY, 1, j2ku_gray_i },
     { "LA", OPJ_CLRSPC_GRAY, 2, j2ku_graya_la },
     { "RGB", OPJ_CLRSPC_GRAY, 1, j2ku_gray_rgb },
     { "RGB", OPJ_CLRSPC_GRAY, 2, j2ku_gray_rgb },
diff --git a/libImaging/Jpeg2KEncode.c b/libImaging/Jpeg2KEncode.c
index 502a0de68..d84ff4f8f 100644
--- a/libImaging/Jpeg2KEncode.c
+++ b/libImaging/Jpeg2KEncode.c
@@ -97,25 +97,8 @@ j2k_pack_i16(Imaging im, UINT8 *buf,
     for (y = 0; y < h; ++y) {
         UINT8 *data = (UINT8 *)(im->image[y + y0] + x0);
         for (x = 0; x < w; ++x) {
-            *ptr++ = data[1];
-            *ptr++ = data[0];
-            data += 2;
-        }
-    }
-}
-
-static void
-j2k_pack_i16b(Imaging im, UINT8 *buf,
-              unsigned x0, unsigned y0, unsigned w, unsigned h)
-{
-    UINT8 *ptr = buf;
-    unsigned x,y;
-    for (y = 0; y < h; ++y) {
-        UINT8 *data = (UINT8 *)(im->image[y + y0] + x0);
-        for (x = 0; x < w; ++x) {
-            *ptr++ = data[0];
-            *ptr++ = data[1];
-            data += 2;
+            *ptr++ = *data++;
+            *ptr++ = *data++;
         }
     }
 }
@@ -310,7 +293,7 @@ j2k_encode_entry(Imaging im, ImagingCodecState state,
     } else if (strcmp (im->mode, "I;16B") == 0) {
         components = 1;
         color_space = OPJ_CLRSPC_GRAY;
-        pack = j2k_pack_i16b;
+        pack = j2k_pack_i16;
         prec = 16;
         bpp = 12;
     } else if (strcmp (im->mode, "LA") == 0) {