diff --git a/Cargo.lock b/Cargo.lock
index da20215e..f84de282 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -385,9 +385,9 @@ dependencies = [
 
 [[package]]
 name = "crossbeam-epoch"
-version = "0.9.18"
+version = "0.9.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+checksum = "2d6914041f254d6e9176c01941b21115dcfb7089e55135a35411081bd106ef3f"
 dependencies = [
  "crossbeam-utils",
 ]
@@ -1037,9 +1037,9 @@ dependencies = [
 
 [[package]]
 name = "libz-sys"
-version = "1.1.25"
+version = "1.1.31"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d52f4c29e2a68ac30c9087e1b772dc9f44a2b66ed44edf2266cf2be9b03dafc1"
+checksum = "ff20308ecabd635a2dc1dd5834a86c462cca20efba1d5d3ddab1f8aea3455cb2"
 dependencies = [
  "cc",
  "cmake",
diff --git a/src/rna/dupradar/counting.rs b/src/rna/dupradar/counting.rs
index 785115c5..11535877 100644
--- a/src/rna/dupradar/counting.rs
+++ b/src/rna/dupradar/counting.rs
@@ -1650,6 +1650,33 @@ pub fn count_reads(
         .filter(|c| c.all_multi > 0)
         .count();
     if merged.total_mapped > 0 && genes_with_reads == 0 {
+        // Only a naming mismatch if no alignment name, after prefix/mapping,
+        // is a GTF chromosome.
+        let shared_chroms: Vec<&str> = tid_to_name
+            .iter()
+            .filter(|bam_name| {
+                let gtf_name = match chrom_mapping.get(bam_name.as_str()) {
+                    Some(mapped) => mapped.clone(),
+                    None => format!("{}{}", chrom_prefix.unwrap_or(""), bam_name),
+                };
+                index.contains_key(&gtf_name)
+            })
+            .take(5)
+            .map(|s| s.as_str())
+            .collect();
+        if !shared_chroms.is_empty() {
+            anyhow::bail!(
+                "No reads could be assigned to any gene under the configured gene-assignment rules \
+                 ({} mapped reads).\n\
+                 \n\
+                 Chromosomes in both the alignment and the GTF (first 5): {}\n\
+                 \n\
+                 The chromosome names match. Check the annotation, genome assembly, and \
+                 strandedness setting for this library.",
+                merged.total_mapped,
+                shared_chroms.join(", ")
+            );
+        }
         let bam_chroms: Vec<&str> = tid_to_name.iter().take(5).map(|s| s.as_str()).collect();
         let gtf_chroms: Vec<&str> = index.keys().take(5).map(|s| s.as_str()).collect();
         anyhow::bail!(
diff --git a/src/rna/rseqc/accumulators.rs b/src/rna/rseqc/accumulators.rs
index b91a409e..d49fae43 100644
--- a/src/rna/rseqc/accumulators.rs
+++ b/src/rna/rseqc/accumulators.rs
@@ -2336,9 +2336,9 @@ fn merge_vec_arrays<const N: usize>(target: &mut Vec<[u64; N]>, source: Vec<[u64
     if source.len() > target.len() {
         target.resize(source.len(), [0u64; N]);
     }
-    for (i, arr) in source.into_iter().enumerate() {
-        for j in 0..N {
-            target[i][j] += arr[j];
+    for (target_row, source_row) in target.iter_mut().zip(source) {
+        for (target_count, source_count) in target_row.iter_mut().zip(source_row) {
+            *target_count += source_count;
         }
     }
 }
diff --git a/src/rna/rseqc/stats.rs b/src/rna/rseqc/stats.rs
index 20abf8c0..96d6444a 100644
--- a/src/rna/rseqc/stats.rs
+++ b/src/rna/rseqc/stats.rs
@@ -525,13 +525,13 @@ fn write_gcc<W: std::io::Write>(
     for cycle in 0..max_cycles {
         let mut combined = [0u64; 6];
         if cycle < fbc.len() {
-            for j in 0..6 {
-                combined[j] += fbc[cycle][j];
+            for (count, &value) in combined.iter_mut().zip(&fbc[cycle]) {
+                *count += value;
             }
         }
         if cycle < lbc.len() {
-            for j in 0..6 {
-                combined[j] += lbc[cycle][j];
+            for (count, &value) in combined.iter_mut().zip(&lbc[cycle]) {
+                *count += value;
             }
         }
         // Denominator is A+C+G+T only (first 4 elements), matching upstream
diff --git a/tests/integration_test.rs b/tests/integration_test.rs
index c7ea3acd..2177d78e 100644
--- a/tests/integration_test.rs
+++ b/tests/integration_test.rs
@@ -1026,3 +1026,166 @@ fn test_dup_check_parallel_uses_global_duplicate_state() {
 
     let _ = fs::remove_dir_all(root);
 }
+
+// ===================================================================
+// No-genic-reads diagnostic
+// ===================================================================
+
+/// Run `rustqc rna` on one mapped read at `bam_chrom:11`, outside the only
+/// gene (`gtf_chrom:900-3000`), with optional YAML config. Returns the output.
+fn run_no_genic_reads(
+    label: &str,
+    bam_chrom: &str,
+    gtf_chrom: &str,
+    config: Option<&str>,
+) -> std::process::Output {
+    let root = unique_test_dir(label);
+    let bam_path = root.join("s.bam");
+    let gtf_path = root.join("a.gtf");
+    let outdir = root.join("out");
+    fs::create_dir_all(&outdir).unwrap();
+    fs::write(
+        &gtf_path,
+        format!(
+            "{gtf_chrom}\tt\tgene\t900\t3000\t.\t+\t.\tgene_id \"g1\"; gene_name \"g1\";\n\
+             {gtf_chrom}\tt\texon\t900\t3000\t.\t+\t.\tgene_id \"g1\"; transcript_id \"t1\"; exon_number \"1\";\n"
+        ),
+    )
+    .unwrap();
+    let read = format!(
+        "r0\t0\t{bam_chrom}\t11\t60\t50M\t*\t0\t0\tACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTAC\t??????????????????????????????????????????????????"
+    );
+    write_bam_fixture(&bam_path, &[(bam_chrom, 100_000)], &[&read]);
+
+    let mut cmd = Command::new(rustqc_binary());
+    cmd.args(["rna", "--skip-dup-check", "--gtf"])
+        .arg(&gtf_path)
+        .arg("--outdir")
+        .arg(&outdir)
+        .arg(&bam_path);
+    if let Some(yaml) = config {
+        let config_path = root.join("config.yaml");
+        fs::write(&config_path, yaml).unwrap();
+        cmd.arg("--config").arg(&config_path);
+    }
+    let output = cmd.output().expect("Failed to execute rustqc");
+    let _ = fs::remove_dir_all(root);
+    output
+}
+
+/// When BAM and GTF share chromosome names but no read lands in a gene,
+/// the error must not claim a naming mismatch. It still fails.
+#[test]
+fn test_no_genic_reads_with_shared_names_is_not_a_name_mismatch() {
+    let output = run_no_genic_reads("no-genic-shared", "chr1", "chr1", None);
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        !output.status.success(),
+        "rustqc should still fail:\n{stderr}"
+    );
+    assert!(
+        !stderr.contains("Chromosome name mismatch"),
+        "BAM and GTF both name chr1, so this is not a name mismatch:\n{stderr}"
+    );
+    assert!(
+        stderr.contains("No reads could be assigned to any gene"),
+        "missing no-assigned-reads diagnostic:\n{stderr}"
+    );
+}
+
+/// Names that only match after `chromosome_prefix` are not a mismatch either.
+#[test]
+fn test_no_genic_reads_with_prefix_mapped_names_is_not_a_name_mismatch() {
+    let output = run_no_genic_reads(
+        "no-genic-prefix",
+        "1",
+        "chr1",
+        Some("rna:\n  chromosome_prefix: \"chr\"\n"),
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        !output.status.success(),
+        "rustqc should still fail:\n{stderr}"
+    );
+    assert!(
+        !stderr.contains("Chromosome name mismatch"),
+        "chromosome_prefix maps 1 to chr1, so this is not a name mismatch:\n{stderr}"
+    );
+    assert!(
+        stderr.contains("No reads could be assigned to any gene"),
+        "missing no-assigned-reads diagnostic:\n{stderr}"
+    );
+}
+
+/// A real naming mismatch (BAM `1`, GTF `chr1`) keeps the mismatch diagnostic.
+#[test]
+fn test_no_genic_reads_with_disjoint_names_is_a_name_mismatch() {
+    let output = run_no_genic_reads("no-genic-disjoint", "1", "chr1", None);
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(!output.status.success(), "rustqc should fail:\n{stderr}");
+    assert!(
+        stderr.contains("Chromosome name mismatch"),
+        "missing chromosome-name diagnostic:\n{stderr}"
+    );
+}
+
+/// A physical gene overlap rejected by strandedness is an assignment failure.
+#[test]
+fn test_no_genic_reads_with_wrong_strand_is_assignment_failure() {
+    let root = unique_test_dir("no-genic-wrong-strand");
+    let bam_path = root.join("s.bam");
+    let gtf_path = root.join("a.gtf");
+    fs::write(
+        &gtf_path,
+        "chr1\tt\tgene\t900\t3000\t.\t+\t.\tgene_id \"g1\"; gene_name \"g1\";\n\
+         chr1\tt\texon\t900\t3000\t.\t+\t.\tgene_id \"g1\"; transcript_id \"t1\"; exon_number \"1\";\n",
+    )
+    .unwrap();
+    let read = format!(
+        "r0\t16\tchr1\t1001\t60\t50M\t*\t0\t0\t{}\t{}",
+        "A".repeat(50),
+        "I".repeat(50)
+    );
+    write_bam_fixture(&bam_path, &[("chr1", 100_000)], &[&read]);
+    let run = |stranded: &str| {
+        Command::new(env!("CARGO_BIN_EXE_rustqc"))
+            .args(["rna", "--skip-dup-check", "--skip-preseq", "--gtf"])
+            .arg(&gtf_path)
+            .args(["--stranded", stranded, "--outdir"])
+            .arg(root.join(stranded))
+            .arg(&bam_path)
+            .output()
+            .expect("Failed to execute rustqc")
+    };
+    let control = run("unstranded");
+    assert!(
+        control.status.success(),
+        "the overlapping read must be assigned in the unstranded control:\n{}",
+        String::from_utf8_lossy(&control.stderr)
+    );
+    let output = run("forward");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        !output.status.success(),
+        "assignment failure must remain fatal:\n{stderr}"
+    );
+    assert!(
+        !stderr.contains("Chromosome name mismatch"),
+        "chromosome names match:\n{stderr}"
+    );
+    assert!(
+        !stderr.contains("overlaps a gene"),
+        "the read overlaps chr1:1001-1050 within g1 at chr1:900-3000; the unstranded control passed:\n{stderr}"
+    );
+    assert!(
+        stderr.contains("configured gene-assignment rules"),
+        "missing assignment-rule diagnostic:\n{stderr}"
+    );
+    assert!(
+        stderr.contains("annotation")
+            && stderr.contains("genome assembly")
+            && stderr.contains("strandedness"),
+        "missing diagnostic guidance:\n{stderr}"
+    );
+    fs::remove_dir_all(root).unwrap();
+}