diff -urNp a/src/lib/OpenEXRUtil/ImfImageChannel.cpp b/src/lib/OpenEXRUtil/ImfImageChannel.cpp
--- a/src/lib/OpenEXRUtil/ImfImageChannel.cpp	2026-06-25 11:16:51.018229425 +0200
+++ b/src/lib/OpenEXRUtil/ImfImageChannel.cpp	2026-06-25 11:18:53.946853720 +0200
@@ -13,6 +13,9 @@
 #include "ImfImageLevel.h"
 #include <Iex.h>
 
+#include <cstdint>
+#include <limits>
+
 using namespace IMATH_NAMESPACE;
 using namespace IEX_NAMESPACE;
 using namespace std;
@@ -54,6 +57,13 @@ ImageChannel::channel () const
 void
 ImageChannel::resize ()
 {
+    if (_xSampling < 1 || _ySampling < 1)
+    {
+        throw ArgExc (
+            "The x and y sampling rates for an image channel must be at "
+            "least 1.");
+    }
+    
     const Box2i& dataWindow = level().dataWindow();
 
     if (dataWindow.min.x % _xSampling || dataWindow.min.y % _ySampling)
@@ -75,7 +85,17 @@ ImageChannel::resize ()
 
     _pixelsPerRow =    width  / _xSampling;
     _pixelsPerColumn = height / _ySampling;
-    _numPixels = _pixelsPerRow * _pixelsPerColumn;
+    
+    const uint64_t w64 = static_cast<uint64_t> (_pixelsPerRow);
+    const uint64_t h64 = static_cast<uint64_t> (_pixelsPerColumn);
+    const uint64_t maxPixels =
+        static_cast<uint64_t> (std::numeric_limits<size_t>::max ());
+    if (w64 != 0 && h64 > maxPixels / w64)
+    {
+        throw ArgExc ("Image channel dimensions too large.");
+    }
+
+    _numPixels = static_cast<size_t> (w64 * h64);
 }
 
 
diff -urNp a/src/test/OpenEXRUtilTest/CMakeLists.txt b/src/test/OpenEXRUtilTest/CMakeLists.txt
--- a/src/test/OpenEXRUtilTest/CMakeLists.txt	2026-06-25 11:16:50.949047862 +0200
+++ b/src/test/OpenEXRUtilTest/CMakeLists.txt	2026-06-25 11:20:16.694600831 +0200
@@ -9,6 +9,8 @@ add_executable(OpenEXRUtilTest
   testDeepImage.h
   testIO.cpp
   testIO.h
+  testImageChannel.cpp
+  testImageChannel.h
  )
 target_include_directories(OpenEXRUtilTest PRIVATE ../OpenEXRTest)
 target_link_libraries(OpenEXRUtilTest OpenEXR::OpenEXRUtil)
@@ -30,4 +32,5 @@ define_openexr_util_tests(
   testFlatImage
   testDeepImage
   testIO
+  testImageChannel
 )
diff -urNp a/src/test/OpenEXRUtilTest/main.cpp b/src/test/OpenEXRUtilTest/main.cpp
--- a/src/test/OpenEXRUtilTest/main.cpp	2026-06-25 11:16:50.949047862 +0200
+++ b/src/test/OpenEXRUtilTest/main.cpp	2026-06-25 11:21:10.550436231 +0200
@@ -11,6 +11,7 @@
 #include "OpenEXRConfigInternal.h"
 
 #include "testFlatImage.h"
+#include "testImageChannel.h"
 #include "testDeepImage.h"
 #include "testIO.h"
 #include "tmpDir.h"
@@ -87,6 +88,7 @@ main (int argc, char *argv[])
     TEST (testFlatImage);
     TEST (testDeepImage);
     TEST (testIO);
+    TEST (testImageChannel);
     // NB: If you add a test here, make sure to enumerate it in the
     // CMakeLists.txt so it runs as part of the test suite
 
diff -urNp a/src/test/OpenEXRUtilTest/testImageChannel.cpp b/src/test/OpenEXRUtilTest/testImageChannel.cpp
--- a/src/test/OpenEXRUtilTest/testImageChannel.cpp	1970-01-01 01:00:00.000000000 +0100
+++ b/src/test/OpenEXRUtilTest/testImageChannel.cpp	2026-06-25 11:21:58.464289792 +0200
@@ -0,0 +1,82 @@
+//
+// SPDX-License-Identifier: BSD-3-Clause
+// Copyright (c) Contributors to the OpenEXR Project.
+//
+
+#ifdef NDEBUG
+#    undef NDEBUG
+#endif
+
+#include "testImageChannel.h"
+
+#include "ImfFlatImage.h"
+
+#include <Iex.h>
+#include <ImathBox.h>
+
+#include <cassert>
+#include <cstring>
+#include <iostream>
+#include <string>
+
+using namespace OPENEXR_IMF_NAMESPACE;
+using namespace IMATH_NAMESPACE;
+using namespace IEX_NAMESPACE;
+using namespace std;
+
+namespace
+{
+
+//
+// Sampling must be >= 1. ImageChannel::resize() rejects non-positive
+// sampling before any modulo or division (so zero cannot invoke undefined
+// behavior). Other invalid cases are still caught later in resize().
+//
+
+void
+expectArgExcOnInsert (const char* label, int xSampling, int ySampling)
+{
+    FlatImage img (Box2i (V2i (0, 0), V2i (3, 3)));
+
+    try
+    {
+        img.insertChannel ("bad", HALF, xSampling, ySampling, false);
+        cerr << "ERROR -- " << label << ": expected ArgExc, insert succeeded"
+             << endl;
+        assert (false);
+    }
+    catch (const ArgExc& e)
+    {
+        // Thrown at the start of ImageChannel::resize() so % and / never use
+        // a zero sampling rate (undefined behavior).
+        assert (strstr (e.what (), "at least 1") != nullptr);
+    }
+}
+
+} // namespace
+
+void
+testImageChannel (const string& tempDir)
+{
+    (void) tempDir;
+
+    try
+    {
+        cout << "Testing ImageChannel sampling constraints" << endl;
+
+        expectArgExcOnInsert ("negative xSampling", -1, 1);
+        expectArgExcOnInsert ("negative ySampling", 1, -1);
+        expectArgExcOnInsert ("negative x and y sampling", -1, -1);
+
+        expectArgExcOnInsert ("zero xSampling", 0, 1);
+        expectArgExcOnInsert ("zero ySampling", 1, 0);
+        expectArgExcOnInsert ("zero x and y sampling", 0, 0);
+
+        cout << "ok\n" << endl;
+    }
+    catch (const std::exception& e)
+    {
+        cerr << "ERROR -- caught exception: " << e.what () << endl;
+        assert (false);
+    }
+}
diff -urNp a/src/test/OpenEXRUtilTest/testImageChannel.h b/src/test/OpenEXRUtilTest/testImageChannel.h
--- a/src/test/OpenEXRUtilTest/testImageChannel.h	1970-01-01 01:00:00.000000000 +0100
+++ b/src/test/OpenEXRUtilTest/testImageChannel.h	2026-06-25 11:22:42.531155111 +0200
@@ -0,0 +1,8 @@
+//
+// SPDX-License-Identifier: BSD-3-Clause
+// Copyright (c) Contributors to the OpenEXR Project.
+//
+
+#include <string>
+
+void testImageChannel (const std::string& tempDir);