diff --git a/parcel.h b/parcel.h
index 2ada709..65320c0 100644
--- a/parcel.h
+++ b/parcel.h
@@ -2329,26 +2329,31 @@ pmd_status pmd_open_series(const char *filename, pmd_series **series_out, pmd_ac
             } else {
                 // Open the HDF5 file
                 file_id = H5Fopen(maybe_padded_iter_filename, H5F_ACC_RDONLY, H5P_DEFAULT);
-                if (file_id >= 0) {
-                    /* Read metadata from the opened file */
-                    status = read_series_metadata_from_file(file_id, series, filename);
-                    if (status != PMD_SUCCESS) {
-                        goto cleanup;
-                    }
-                    maybe_padded_file = maybe_padded_iter_filename;
+                if (file_id < 0) {
+                    pmd_log(PMD_LOG_ERROR, "Failed to open '%s' (matched pattern '%s') as HDF5",
+                            maybe_padded_iter_filename, filename);
+                    status = PMD_ERROR_HDF5;
+                    goto cleanup;
+                }
 
-                    /* A %T filename pattern is only valid for file-based series */
-                    if (series->iteration_encoding != PMD_FILE_BASED) {
-                        pmd_log(PMD_LOG_ERROR, "File '%s' matched pattern '%s' but is not a fileBased series",
-                                maybe_padded_iter_filename, filename);
-                        status = PMD_ERROR_FILE_FORMAT;
-                        goto cleanup;
-                    }
+                /* Read metadata from the opened file */
+                status = read_series_metadata_from_file(file_id, series, filename);
+                if (status != PMD_SUCCESS) {
+                    goto cleanup;
+                }
+                maybe_padded_file = maybe_padded_iter_filename;
 
-                    /* Close file since we will not store for file-based mode */
-                    H5Fclose(file_id);
-                    file_id = -1;
+                /* A %T filename pattern is only valid for file-based series */
+                if (series->iteration_encoding != PMD_FILE_BASED) {
+                    pmd_log(PMD_LOG_ERROR, "File '%s' matched pattern '%s' but is not a fileBased series",
+                            maybe_padded_iter_filename, filename);
+                    status = PMD_ERROR_FILE_FORMAT;
+                    goto cleanup;
                 }
+
+                /* Close file since we will not store for file-based mode */
+                H5Fclose(file_id);
+                file_id = -1;
             }
 
             /* Set directory from pattern if not already set */
diff --git a/tests/test_write.c b/tests/test_write.c
index 7ab21f5..3b3455a 100644
--- a/tests/test_write.c
+++ b/tests/test_write.c
@@ -1009,6 +1009,29 @@ void test_invalid_pattern_ambiguous(void) {
     TEST_ASSERT_NOT_EQUAL(PMD_SUCCESS, result);
 }
 
+/**
+ * Test: %T filename pattern that matches a file HDF5 cannot open fails
+ */
+void test_pattern_open_invalid_hdf5_fails(void) {
+    pmd_series *series;
+    pmd_status result;
+
+    /* Create a file whose name matches bad_%T.h5 but is not HDF5 */
+    FILE *bad_file = fopen(TEST_TEMP_DIR "/bad_0.h5", "wb");
+    TEST_ASSERT_NOT_NULL(bad_file);
+    TEST_ASSERT_TRUE(fputs("not an hdf5 file\n", bad_file) >= 0);
+    TEST_ASSERT_EQUAL_INT(0, fclose(bad_file));
+
+    /* Read-only must be checked first: RDWR writes root attributes during open */
+    result = pmd_open_series(TEST_TEMP_DIR "/bad_%T.h5", &series, PMD_RDONLY);
+    TEST_ASSERT_EQUAL_INT(PMD_ERROR_HDF5, result);
+    TEST_ASSERT_NULL(series);
+
+    result = pmd_open_series(TEST_TEMP_DIR "/bad_%T.h5", &series, PMD_RDWR);
+    TEST_ASSERT_EQUAL_INT(PMD_ERROR_HDF5, result);
+    TEST_ASSERT_NULL(series);
+}
+
 /**
  * Test: %T filename pattern that matches a group-based file fails
  */
@@ -2730,6 +2753,7 @@ int main(void) {
     RUN_TEST(test_write_nonconsecutive_iterations_file_based);
     RUN_TEST(test_write_fails_no_parent_directory);
     RUN_TEST(test_invalid_pattern_ambiguous);
+    RUN_TEST(test_pattern_open_invalid_hdf5_fails);
     RUN_TEST(test_pattern_matching_group_based_file_fails);
     RUN_TEST(test_valid_filebased_patterns);
     RUN_TEST(test_truncate_deletes_existing_files);