diff --git a/PIL/WebPImagePlugin.py b/PIL/WebPImagePlugin.py
index cdf5fe48e..afddb0a0d 100644
--- a/PIL/WebPImagePlugin.py
+++ b/PIL/WebPImagePlugin.py
@@ -157,6 +157,11 @@ class WebPImageFile(ImageFile.ImageFile):
                       # Decoder params: rawmode, has_alpha, width, height.
                       (mode, 1 if 'RGBA' == mode else 0, size[0], size[1]))]
 
+        if not lossy:
+            # Incremental decoding on lossless is *really* slow, disable it.
+            self.decodermaxblock = 12 + i32le(header[4:8])
+            self.decoderconfig = (1,)
+
     def draft(self, mode, size):
 
         if 1 != len(self.tile):
diff --git a/decode.c b/decode.c
index 2aab01157..782966ac4 100644
--- a/decode.c
+++ b/decode.c
@@ -740,10 +740,12 @@ PyImaging_WebPDecoderNew(PyObject* self, PyObject* args)
     char* rawmode; /* what we wan't from the decoder */
     int has_alpha;
     int width, height;
+    int onepass = 0;
 
-    if (!PyArg_ParseTuple(args, "ssiii",
+    if (!PyArg_ParseTuple(args, "ssiii|i",
                           &mode, &rawmode,
-                          &has_alpha, &width, &height))
+                          &has_alpha, &width, &height,
+                          &onepass))
         return NULL;
 
     decoder = PyImaging_DecoderNew(sizeof(WEBPSTATE));
@@ -763,6 +765,7 @@ PyImaging_WebPDecoderNew(PyObject* self, PyObject* args)
     context->has_alpha = has_alpha;
     context->width = width;
     context->height = height;
+    context->onepass = onepass;
     context->output = NULL;
     context->decoder = NULL;
 
diff --git a/libImaging/WebP.h b/libImaging/WebP.h
index 7da292e6f..6eb9b51bb 100644
--- a/libImaging/WebP.h
+++ b/libImaging/WebP.h
@@ -22,6 +22,9 @@ typedef struct {
     int has_alpha;
     int width, height;
 
+    /* Decoder will receive and decode the data in one pass. */
+    int onepass;
+
     /* PRIVATE CONTEXT (set by decoder) */
 
     WebPDecoderConfig  config;
diff --git a/libImaging/WebPDecode.c b/libImaging/WebPDecode.c
index c886ffc94..9b19b764e 100644
--- a/libImaging/WebPDecode.c
+++ b/libImaging/WebPDecode.c
@@ -81,24 +81,39 @@ int ImagingWebPDecode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes
             config->options.use_scaling = 1;
         }
 
-        context->decoder = WebPIDecode(NULL, 0, config);
-        if (NULL == context->decoder)
+        if (!context->onepass)
         {
-            state->errcode = _vp8_status_to_codec_status(vp8_status_code);
-            return -1;
+            context->decoder = WebPIDecode(NULL, 0, config);
+            if (NULL == context->decoder)
+            {
+                state->errcode = _vp8_status_to_codec_status(vp8_status_code);
+                return -1;
+            }
         }
 
         state->state = 1;
     }
 
-    /* Consume the buffer, decoding as much as possible. */
-    vp8_status_code = WebPIAppend(context->decoder, buf, bytes);
-    if (VP8_STATUS_NOT_ENOUGH_DATA != vp8_status_code &&
-        VP8_STATUS_SUSPENDED != vp8_status_code &&
-        VP8_STATUS_OK != vp8_status_code)
+    if (context->onepass)
     {
-        state->errcode = _vp8_status_to_codec_status(vp8_status_code);
-        return -1;
+        vp8_status_code = WebPDecode(buf, bytes, config);
+        if (VP8_STATUS_OK != vp8_status_code)
+        {
+            state->errcode = _vp8_status_to_codec_status(vp8_status_code);
+            return -1;
+        }
+    }
+    else
+    {
+        /* Consume the buffer, decoding as much as possible. */
+        vp8_status_code = WebPIAppend(context->decoder, buf, bytes);
+        if (VP8_STATUS_NOT_ENOUGH_DATA != vp8_status_code &&
+            VP8_STATUS_SUSPENDED != vp8_status_code &&
+            VP8_STATUS_OK != vp8_status_code)
+        {
+            state->errcode = _vp8_status_to_codec_status(vp8_status_code);
+            return -1;
+        }
     }
 
     if (VP8_STATUS_NOT_ENOUGH_DATA != vp8_status_code)
@@ -111,7 +126,19 @@ int ImagingWebPDecode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes
         int            height;
         int            stride;
 
-        rgba = WebPIDecGetRGB(context->decoder, &last_y, &width, &height, &stride);
+        if (context->onepass)
+        {
+            rgba = config->output.u.RGBA.rgba;
+            last_y = state->ysize;
+            width = state->xsize;
+            height = state->ysize;
+            stride = config->output.u.RGBA.stride;
+        }
+        else
+        {
+            rgba = WebPIDecGetRGB(context->decoder, &last_y, &width, &height, &stride);
+        }
+
         if (NULL != rgba)
         {
             assert(width == state->xsize);