diff --git a/src/jpegxl.imageio/jxlinput.cpp b/src/jpegxl.imageio/jxlinput.cpp
index 3ac507fe80..9e268ca74f 100644
--- a/src/jpegxl.imageio/jxlinput.cpp
+++ b/src/jpegxl.imageio/jxlinput.cpp
@@ -208,6 +208,10 @@ JxlInput::open(const std::string& name, ImageSpec& newspec)
         jxl.reset(new uint8_t[size]);
         size_t result = m_io->read(jxl.get(), size);
         DBG std::cout << "result = " << result << "\n";
+        if (result != size) {
+            errorfmt("Failed to read {} bytes from \"{}\"", size, m_filename);
+            return false;
+        }
 
         status = JxlDecoderSetInput(m_decoder.get(), jxl.get(), size);
         if (status != JXL_DEC_SUCCESS) {
@@ -340,10 +344,11 @@ JxlInput::open(const std::string& name, ImageSpec& newspec)
                 errorfmt("JxlDecoderImageOutBufferSize failed\n");
                 return false;
             }
-            if (buffer_size
-                != info.xsize * info.ysize * m_channels * bits / 8) {
+            size_t expected_size = size_t(info.xsize) * info.ysize * m_channels
+                                   * bits / 8;
+            if (buffer_size != expected_size) {
                 errorfmt("Invalid out buffer size {} {}\n", buffer_size,
-                         info.xsize * info.ysize * m_channels * bits / 8);
+                         expected_size);
                 return false;
             }
 
@@ -381,6 +386,15 @@ JxlInput::open(const std::string& name, ImageSpec& newspec)
         return false;
     }
 
+    // A valid image always triggers JXL_DEC_NEED_IMAGE_OUT_BUFFER and allocates
+    // m_buffer during the decode loop above. If it didn't, the file provided
+    // basic info but no decodable pixels; fail rather than let a later
+    // read_native_scanline() dereference a null buffer.
+    if (!m_buffer) {
+        errorfmt("Possible corrupt file, no JPEG XL image data decoded\n");
+        return false;
+    }
+
     // Read ICC profile
     if (m_icc_profile.size() && m_icc_profile.data()) {
         m_spec.attribute("ICCProfile",
diff --git a/testsuite/jxl/ref/out-jxl0.12.txt b/testsuite/jxl/ref/out-jxl0.12.txt
index bcacb63c91..4c63c7c9ae 100644
--- a/testsuite/jxl/ref/out-jxl0.12.txt
+++ b/testsuite/jxl/ref/out-jxl0.12.txt
@@ -91,3 +91,6 @@ oiiotool ERROR: read : "src/crash-bfd2220.jxl": jpegxl image dimension 328438676
 If you're sure this is a valid file, raise the OIIO global attribute "limits:resolution".
 Full command line was:
 > oiiotool -info -oiioattrib limits:imagesize_MB 16384 src/crash-bfd2220.jxl
+oiiotool ERROR: read : "src/truncated.jxl": JPEG XL decoder error
+Full command line was:
+> oiiotool --info -v -a --no-metamatch DateTime|Software|OriginatingProgram|ImageHistory --hash src/truncated.jxl
diff --git a/testsuite/jxl/ref/out.txt b/testsuite/jxl/ref/out.txt
index 625b1288e3..9edf3492d2 100644
--- a/testsuite/jxl/ref/out.txt
+++ b/testsuite/jxl/ref/out.txt
@@ -91,3 +91,6 @@ oiiotool ERROR: read : "src/crash-bfd2220.jxl": jpegxl image dimension 328438676
 If you're sure this is a valid file, raise the OIIO global attribute "limits:resolution".
 Full command line was:
 > oiiotool -info -oiioattrib limits:imagesize_MB 16384 src/crash-bfd2220.jxl
+oiiotool ERROR: read : "src/truncated.jxl": JPEG XL decoder error
+Full command line was:
+> oiiotool --info -v -a --no-metamatch DateTime|Software|OriginatingProgram|ImageHistory --hash src/truncated.jxl
diff --git a/testsuite/jxl/run.py b/testsuite/jxl/run.py
index e6b05d30eb..6bb2a673a7 100755
--- a/testsuite/jxl/run.py
+++ b/testsuite/jxl/run.py
@@ -24,6 +24,10 @@
 # Corrupt input that previously triggered an oversized allocation path in JXL decode
 command += oiiotool ("-info -oiioattrib limits:imagesize_MB 16384 src/crash-bfd2220.jxl", failureok=True)
 
+# Truncated codestream: the decoder must report a clean error, not read
+# uninitialized input or leave a null decode buffer for a later scanline read.
+command += info_command ("src/truncated.jxl", failureok=True, safematch=True)
+
 outputs = [
             "test-jxl.icc",
             "out.txt"
diff --git a/testsuite/jxl/src/truncated.jxl b/testsuite/jxl/src/truncated.jxl
new file mode 100644
index 0000000000..6f7714b738
Binary files /dev/null and b/testsuite/jxl/src/truncated.jxl differ