diff --git a/Tests/test_image_putdata.py b/Tests/test_image_putdata.py
index 54712fd6c..7e4bbaaec 100644
--- a/Tests/test_image_putdata.py
+++ b/Tests/test_image_putdata.py
@@ -1,6 +1,8 @@
 import sys
 from array import array
 
+import pytest
+
 from PIL import Image
 
 from .helper import assert_image_equal, hopper
@@ -47,6 +49,12 @@ def test_pypy_performance():
     im.putdata(list(range(256)) * 256)
 
 
+def test_mode_with_L_with_float():
+    im = Image.new("L", (1, 1), 0)
+    im.putdata([2.0])
+    assert im.getpixel((0, 0)) == 2
+
+
 def test_mode_i():
     src = hopper("L")
     data = list(src.getdata())
@@ -87,3 +95,18 @@ def test_array_F():
     im.putdata(arr)
 
     assert len(im.getdata()) == len(arr)
+
+
+def test_not_flattened():
+    im = Image.new("L", (1, 1))
+    with pytest.raises(TypeError):
+        im.putdata([[0]])
+    with pytest.raises(TypeError):
+        im.putdata([[0]], 2)
+
+    with pytest.raises(TypeError):
+        im = Image.new("I", (1, 1))
+        im.putdata([[0]])
+    with pytest.raises(TypeError):
+        im = Image.new("F", (1, 1))
+        im.putdata([[0]])
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 3fa0d7cad..3631bd869 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -1705,13 +1705,14 @@ class Image:
 
     def putdata(self, data, scale=1.0, offset=0.0):
         """
-        Copies pixel data to this image.  This method copies data from a
-        sequence object into the image, starting at the upper left
-        corner (0, 0), and continuing until either the image or the
-        sequence ends.  The scale and offset values are used to adjust
-        the sequence values: **pixel = value*scale + offset**.
+        Copies pixel data from a flattened sequence object into the image. The
+        values should start at the upper left corner (0, 0), continue to the
+        end of the line, followed directly by the first value of the second
+        line, and so on. Data will be read until either the image or the
+        sequence ends. The scale and offset values are used to adjust the
+        sequence values: **pixel = value*scale + offset**.
 
-        :param data: A sequence object.
+        :param data: A flattened sequence object.
         :param scale: An optional scale value.  The default is 1.0.
         :param offset: An optional offset value.  The default is 0.0.
         """
diff --git a/src/_imaging.c b/src/_imaging.c
index aba907f88..2a42c0461 100644
--- a/src/_imaging.c
+++ b/src/_imaging.c
@@ -1494,6 +1494,14 @@ _putdata(ImagingObject *self, PyObject *args) {
         return NULL;
     }
 
+#define set_value_to_item(seq, i) \
+op = PySequence_Fast_GET_ITEM(seq, i); \
+if (PySequence_Check(op)) { \
+    PyErr_SetString(PyExc_TypeError, "sequence must be flattened"); \
+    return NULL; \
+} else { \
+    value = PyFloat_AsDouble(op); \
+}
     if (image->image8) {
         if (PyBytes_Check(data)) {
             unsigned char *p;
@@ -1522,11 +1530,12 @@ _putdata(ImagingObject *self, PyObject *args) {
                 PyErr_SetString(PyExc_TypeError, must_be_sequence);
                 return NULL;
             }
+            double value;
             if (scale == 1.0 && offset == 0.0) {
                 /* Clipped data */
                 for (i = x = y = 0; i < n; i++) {
-                    op = PySequence_Fast_GET_ITEM(seq, i);
-                    image->image8[y][x] = (UINT8)CLIP8(PyLong_AsLong(op));
+                    set_value_to_item(seq, i);
+                    image->image8[y][x] = (UINT8)CLIP8(value);
                     if (++x >= (int)image->xsize) {
                         x = 0, y++;
                     }
@@ -1535,9 +1544,8 @@ _putdata(ImagingObject *self, PyObject *args) {
             } else {
                 /* Scaled and clipped data */
                 for (i = x = y = 0; i < n; i++) {
-                    PyObject *op = PySequence_Fast_GET_ITEM(seq, i);
-                    image->image8[y][x] =
-                        CLIP8((int)(PyFloat_AsDouble(op) * scale + offset));
+                    set_value_to_item(seq, i);
+                    image->image8[y][x] = CLIP8(value * scale + offset);
                     if (++x >= (int)image->xsize) {
                         x = 0, y++;
                     }
@@ -1555,9 +1563,10 @@ _putdata(ImagingObject *self, PyObject *args) {
         switch (image->type) {
             case IMAGING_TYPE_INT32:
                 for (i = x = y = 0; i < n; i++) {
-                    op = PySequence_Fast_GET_ITEM(seq, i);
+                    double value;
+                    set_value_to_item(seq, i);
                     IMAGING_PIXEL_INT32(image, x, y) =
-                        (INT32)(PyFloat_AsDouble(op) * scale + offset);
+                        (INT32)(value * scale + offset);
                     if (++x >= (int)image->xsize) {
                         x = 0, y++;
                     }
@@ -1566,9 +1575,10 @@ _putdata(ImagingObject *self, PyObject *args) {
                 break;
             case IMAGING_TYPE_FLOAT32:
                 for (i = x = y = 0; i < n; i++) {
-                    op = PySequence_Fast_GET_ITEM(seq, i);
+                    double value;
+                    set_value_to_item(seq, i);
                     IMAGING_PIXEL_FLOAT32(image, x, y) =
-                        (FLOAT32)(PyFloat_AsDouble(op) * scale + offset);
+                        (FLOAT32)(value * scale + offset);
                     if (++x >= (int)image->xsize) {
                         x = 0, y++;
                     }