diff --git a/_imaging.c b/_imaging.c
index 610710bd1..6276bc678 100644
--- a/_imaging.c
+++ b/_imaging.c
@@ -1366,7 +1366,7 @@ _putpalette(ImagingObject* self, PyObject* args)
     char* rawmode;
     UINT8* palette;
     int palettesize;
-    if (!PyArg_ParseTuple(args, "ss#", &rawmode, &palette, &palettesize))
+    if (!PyArg_ParseTuple(args, "s"PY_ARG_BYTES_LENGTH, &rawmode, &palette, &palettesize))
 	return NULL;
 
     if (strcmp(self->image->mode, "L") != 0 && strcmp(self->image->mode, "P")) {
@@ -1861,8 +1861,9 @@ _getprojection(ImagingObject* self, PyObject* args)
 
     ImagingGetProjection(self->image, (unsigned char *)xprofile, (unsigned char *)yprofile);
 
-    result = Py_BuildValue("s#s#", xprofile, self->image->xsize,
-			   yprofile, self->image->ysize);
+    result = Py_BuildValue(PY_ARG_BYTES_LENGTH PY_ARG_BYTES_LENGTH,
+                           xprofile, self->image->xsize,
+                           yprofile, self->image->ysize);
 
     free(xprofile);
     free(yprofile);
@@ -2089,7 +2090,7 @@ _font_new(PyObject* self_, PyObject* args)
     ImagingObject* imagep;
     unsigned char* glyphdata;
     int glyphdata_length;
-    if (!PyArg_ParseTuple(args, "O!s#",
+    if (!PyArg_ParseTuple(args, "O!"PY_ARG_BYTES_LENGTH,
 			  &Imaging_Type, &imagep,
 			  &glyphdata, &glyphdata_length))
         return NULL;
@@ -2787,7 +2788,8 @@ _crc32(PyObject* self, PyObject* args)
 
     hi = lo = 0;
 
-    if (!PyArg_ParseTuple(args, "s#|(ii)", &buffer, &bytes, &hi, &lo))
+    if (!PyArg_ParseTuple(args, PY_ARG_BYTES_LENGTH"|(ii)",
+                          &buffer, &bytes, &hi, &lo))
 	return NULL;
 
     crc = ((UINT32) (hi & 0xFFFF) << 16) + (lo & 0xFFFF);
diff --git a/_imagingcms.c b/_imagingcms.c
index 693de5c3b..910dc6eeb 100644
--- a/_imagingcms.c
+++ b/_imagingcms.c
@@ -129,8 +129,13 @@ cms_profile_fromstring(PyObject* self, PyObject* args)
 
     char* pProfile;
     int nProfile;
+#if PY_VERSION_HEX >= 0x03000000
+    if (!PyArg_ParseTuple(args, "y#:profile_frombytes", &pProfile, &nProfile))
+        return NULL;
+#else
     if (!PyArg_ParseTuple(args, "s#:profile_fromstring", &pProfile, &nProfile))
         return NULL;
+#endif
 
     cmsErrorAction(LCMS_ERROR_IGNORE);
 
@@ -496,7 +501,11 @@ cms_get_display_profile_win32(PyObject* self, PyObject* args)
 static PyMethodDef pyCMSdll_methods[] = {
 
     {"profile_open", cms_profile_open, 1},
+#if PY_VERSION_HEX >= 0x03000000
+    {"profile_frombytes", cms_profile_fromstring, 1},
+#else
     {"profile_fromstring", cms_profile_fromstring, 1},
+#endif
 
     /* profile and transform functions */
     {"buildTransform", buildTransform, 1},
diff --git a/decode.c b/decode.c
index 6f5fe278f..0b2be8dfd 100644
--- a/decode.c
+++ b/decode.c
@@ -37,6 +37,7 @@
 #endif
 
 #include "Imaging.h"
+#include "py3.h"
 
 #include "Gif.h"
 #include "Lzw.h"
@@ -111,7 +112,7 @@ _decode(ImagingDecoderObject* decoder, PyObject* args)
     UINT8* buffer;
     int bufsize, status;
 
-    if (!PyArg_ParseTuple(args, "s#", &buffer, &bufsize))
+    if (!PyArg_ParseTuple(args, PY_ARG_BYTES_LENGTH, &buffer, &bufsize))
 	return NULL;
 
     status = decoder->decode(decoder->im, &decoder->state, buffer, bufsize);
diff --git a/display.c b/display.c
index b334fbc95..9571b1cbe 100644
--- a/display.c
+++ b/display.c
@@ -31,6 +31,7 @@
 #endif
 
 #include "Imaging.h"
+#include "py3.h"
 
 /* -------------------------------------------------------------------- */
 /* Windows DIB support	*/
@@ -183,8 +184,14 @@ _fromstring(ImagingDisplayObject* display, PyObject* args)
 {
     char* ptr;
     int bytes;
+
+#if PY_VERSION_HEX >= 0x03000000
+    if (!PyArg_ParseTuple(args, "y#:frombytes", &ptr, &bytes))
+        return NULL;
+#else
     if (!PyArg_ParseTuple(args, "s#:fromstring", &ptr, &bytes))
-	return NULL;
+        return NULL;
+#endif
 
     if (display->dib->ysize * display->dib->linesize != bytes) {
         PyErr_SetString(PyExc_ValueError, "wrong size");
@@ -200,10 +207,15 @@ _fromstring(ImagingDisplayObject* display, PyObject* args)
 static PyObject*
 _tostring(ImagingDisplayObject* display, PyObject* args)
 {
+#if PY_VERSION_HEX >= 0x03000000
+    if (!PyArg_ParseTuple(args, ":tobytes"))
+        return NULL;
+#else
     if (!PyArg_ParseTuple(args, ":tostring"))
-	return NULL;
+        return NULL;
+#endif
 
-    return PyString_FromStringAndSize(
+    return PyBytes_FromStringAndSize(
         display->dib->bits, display->dib->ysize * display->dib->linesize
         );
 }
@@ -215,8 +227,13 @@ static struct PyMethodDef methods[] = {
     {"query_palette", (PyCFunction)_query_palette, 1},
     {"getdc", (PyCFunction)_getdc, 1},
     {"releasedc", (PyCFunction)_releasedc, 1},
+#if PY_VERSION_HEX >= 0x03000000
+    {"frombytes", (PyCFunction)_fromstring, 1},
+    {"tobytes", (PyCFunction)_tostring, 1},
+#else
     {"fromstring", (PyCFunction)_fromstring, 1},
     {"tostring", (PyCFunction)_tostring, 1},
+#endif
     {NULL, NULL} /* sentinel */
 };
 
@@ -771,7 +788,7 @@ PyImaging_DrawWmf(PyObject* self, PyObject* args)
     int datasize;
     int width, height;
     int x0, y0, x1, y1;
-    if (!PyArg_ParseTuple(args, "s#(ii)(iiii):_load", &data, &datasize,
+    if (!PyArg_ParseTuple(args, PY_ARG_BYTES_LENGTH"(ii)(iiii):_load", &data, &datasize,
                           &width, &height, &x0, &x1, &y0, &y1))
         return NULL;
 
diff --git a/encode.c b/encode.c
index 939fc6b93..670bd7dc9 100644
--- a/encode.c
+++ b/encode.c
@@ -30,6 +30,7 @@
 #endif
 
 #include "Imaging.h"
+#include "py3.h"
 #include "Gif.h"
 
 #ifdef HAVE_UNISTD_H
@@ -451,9 +452,21 @@ PyImaging_ZipEncoderNew(PyObject* self, PyObject* args)
     int optimize = 0;
     char* dictionary = NULL;
     int dictionary_size = 0;
-    if (!PyArg_ParseTuple(args, "ss|is#", &mode, &rawmode, &optimize,
-			  &dictionary, &dictionary_size))
-	return NULL;
+    if (!PyArg_ParseTuple(args, "ss|i"PY_ARG_BYTES_LENGTH, &mode, &rawmode,
+                          &optimize, &dictionary, &dictionary_size))
+        return NULL;
+
+    /* Copy to avoid referencing Python's memory, but there's no mechanism to
+       free this memory later, so this function (and several others here)
+       leaks. */
+    if (dictionary && dictionary_size > 0) {
+        char* p = malloc(dictionary_size);
+        if (!p)
+            return PyErr_NoMemory();
+        memcpy(p, dictionary, dictionary_size);
+        dictionary = p;
+    } else
+        dictionary = NULL;
 
     encoder = PyImaging_EncoderNew(sizeof(ZIPSTATE));
     if (encoder == NULL)
@@ -513,8 +526,9 @@ PyImaging_JpegEncoderNew(PyObject* self, PyObject* args)
     int xdpi = 0, ydpi = 0;
     int subsampling = -1; /* -1=default, 0=none, 1=medium, 2=high */
     char* extra = NULL; int extra_size;
-    if (!PyArg_ParseTuple(args, "ss|iiiiiiiis#", &mode, &rawmode, &quality,
-			  &progressive, &smooth, &optimize, &streamtype,
+    if (!PyArg_ParseTuple(args, "ss|iiiiiiii"PY_ARG_BYTES_LENGTH,
+                          &mode, &rawmode, &quality,
+                          &progressive, &smooth, &optimize, &streamtype,
                           &xdpi, &ydpi, &subsampling, &extra, &extra_size))
 	return NULL;
 
diff --git a/py3.h b/py3.h
index a0054bb46..e0658b0bb 100644
--- a/py3.h
+++ b/py3.h
@@ -11,13 +11,16 @@
 */
 
 #if PY_VERSION_HEX >= 0x03000000
+#define PY_ARG_BYTES_LENGTH             "y#"
+
 /* Map PyInt -> PyLong */
 #define PyInt_AsLong                PyLong_AsLong
 #define PyInt_Check                 PyLong_Check
 #define PyInt_FromLong              PyLong_FromLong
 #define PyInt_AS_LONG               PyLong_AS_LONG
 
-#else
+#else   /* PY_VERSION_HEX < 0x03000000 */
+#define PY_ARG_BYTES_LENGTH             "s#"
 
 #if !defined(KEEP_PY_UNICODE)
 /* Map PyUnicode -> PyString */