diff --git a/src/dpx.imageio/libdpx/ReaderInternal.h b/src/dpx.imageio/libdpx/ReaderInternal.h
index 124f9405a6..74899ab09e 100644
--- a/src/dpx.imageio/libdpx/ReaderInternal.h
+++ b/src/dpx.imageio/libdpx/ReaderInternal.h
@@ -172,7 +172,8 @@ namespace dpx
 			BUF *obuf = data + bufoff;
 			int index = (block.x1 * sizeof(U32)) % numberOfComponents;
 
-			for (int count = (block.x2 - block.x1 + 1) * numberOfComponents - 1; count >= 0; count--)
+			const int total = (block.x2 - block.x1 + 1) * numberOfComponents;
+			for (int count = total - 1; count >= 0; count--)
 			{
 				// unpacking the buffer backwards
 				U16 d1 = U16(readBuf[(count + index) / 3] >> ((2 - (count + index) % 3) * 10 + PADDINGBITS) & 0x3ff);
@@ -181,7 +182,10 @@ namespace dpx
 				BaseTypeConverter(d1, obuf[count]);
 
 				// work-around for 1-channel DPX images - to swap the outlying pixels, otherwise the columns are in the wrong order
-				if (numberOfComponents == 1 && count % 3 == 0)
+				// Only when a full group of 3 remains in bounds -- a short trailing
+				// group (when total isn't a multiple of 3) has no third datum to
+				// swap with, and obuf[count + 2] would be out of bounds.
+				if (numberOfComponents == 1 && count % 3 == 0 && count + 2 < total)
 					std::swap(obuf[count], obuf[count + 2]);
 			}
 #endif		
diff --git a/testsuite/dpx/ref/out.txt b/testsuite/dpx/ref/out.txt
index 88458509f1..d4c13b5d2e 100644
--- a/testsuite/dpx/ref/out.txt
+++ b/testsuite/dpx/ref/out.txt
@@ -161,3 +161,61 @@ PASS
 oiiotool ERROR: read : "src/crash-badusersize.dpx": Corrupt userbuf: size claims 4160749568 but whole file size is 2054
 Full command line was:
 > oiiotool src/crash-badusersize.dpx -o test.tif
+Reading src/crash-1chan-10bit-filled-methodA.dpx
+src/crash-1chan-10bit-filled-methodA.dpx :   80 x   60, 3 channel, uint10 dpx
+    2 subimages: 80x60 [u10,u10,u10], 80x60 [u10]
+ subimage  0:   80 x   60, 3 channel, uint10 dpx
+    SHA-1: 0071FD79957267E8C9978DB3360AF9C752E31556
+    channel list: R, G, B
+    full/display size: 2143289344 x 2143289344
+    full/display origin: 0, 0
+    ImageDescription: "view angle: left"
+    Orientation: 1 (normal)
+    PixelAspectRatio: 1
+    dpx:Colorimetric: "User defined"
+    dpx:DittoKey: 1
+    dpx:EndOfImagePadding: 0
+    dpx:EndOfLinePadding: 0
+    dpx:FramePosition: 0
+    dpx:ImageDescriptor: "RGB"
+    dpx:Packing: "Filled, method A"
+    dpx:SequenceLength: 0
+    dpx:SourceImageFileName: "P"
+    dpx:TimeCode: "00:00:00:00"
+    dpx:Transfer: "Undefined"
+    dpx:UserBits: 0
+    dpx:Version: "V2.0"
+    dpx:VerticalSampleRate: -1.7147e+38
+    dpx:XScannedSize: 1.4013e-45
+    dpx:YScannedSize: 1.4013e-45
+    oiio:BitsPerSample: 10
+    oiio:subimages: 2
+    smpte:TimeCode: 00:00:00:00
+ subimage  1:   80 x   60, 1 channel, uint10 dpx
+    SHA-1: 26C5096595B63C5BF3AC347712B11353BB55F1EC
+    channel list: channel0
+    full/display size: 2143289344 x 2143289344
+    full/display origin: 0, 0
+    ImageDescription: "view angle: left"
+    Orientation: 1 (normal)
+    PixelAspectRatio: 1
+    dpx:Colorimetric: "User defined"
+    dpx:DittoKey: 1
+    dpx:EndOfImagePadding: 0
+    dpx:EndOfLinePadding: 0
+    dpx:FramePosition: 0
+    dpx:HighQuantity: 7.57306e-29
+    dpx:ImageDescriptor: "User defined"
+    dpx:Packing: "Filled, method A"
+    dpx:SequenceLength: 0
+    dpx:SourceImageFileName: "P"
+    dpx:TimeCode: "00:00:00:00"
+    dpx:Transfer: "User defined"
+    dpx:UserBits: 0
+    dpx:Version: "V2.0"
+    dpx:VerticalSampleRate: -1.7147e+38
+    dpx:XScannedSize: 1.4013e-45
+    dpx:YScannedSize: 1.4013e-45
+    oiio:BitsPerSample: 10
+    oiio:subimages: 2
+    smpte:TimeCode: 00:00:00:00
diff --git a/testsuite/dpx/run.py b/testsuite/dpx/run.py
index 536e705927..1acaee89e7 100755
--- a/testsuite/dpx/run.py
+++ b/testsuite/dpx/run.py
@@ -37,3 +37,11 @@
 
 # Regression tests
 command += oiiotool("src/crash-badusersize.dpx -o test.tif", failureok=True)
+
+# Regression test: crafted DPX with a 1-channel, 10-bit, "Filled method A"
+# packed subimage whose width (80) is not a multiple of 3. The 1-channel
+# work-around in Read10bitFilled() swapped the first and third datum of
+# each group of 3 packed samples, but did not check that a full group of 3
+# remained for the last (partial) group in the scanline, writing/reading
+# one uint16 past the end of the caller's scanline buffer.
+command += info_command("src/crash-1chan-10bit-filled-methodA.dpx", safematch=True)
diff --git a/testsuite/dpx/src/crash-1chan-10bit-filled-methodA.dpx b/testsuite/dpx/src/crash-1chan-10bit-filled-methodA.dpx
new file mode 100644
index 0000000000..50579aeab1
Binary files /dev/null and b/testsuite/dpx/src/crash-1chan-10bit-filled-methodA.dpx differ