diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b8aba65..a47b02f1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+### Performance
+- Faster runtime-error detection: single `case` glob instead of 23-iteration loop in `detect_runtime_error` (#668)
+
 ## [0.36.0](https://github.com/TypedDevs/bashunit/compare/0.35.0...0.36.0) - 2026-05-07
 
 ### Fixed
diff --git a/src/runner.sh b/src/runner.sh
index 34abaf24..be5cdcbf 100755
--- a/src/runner.sh
+++ b/src/runner.sh
@@ -72,7 +72,7 @@ function bashunit::runner::compute_total_assertions() {
   incomplete="${incomplete%%##*}"
   snapshot="${test_execution_result##*##ASSERTIONS_SNAPSHOT=}"
   snapshot="${snapshot%%##*}"
-  printf '%d' "$(( ${failed:-0} + ${passed:-0} + ${skipped:-0} + ${incomplete:-0} + ${snapshot:-0} ))"
+  printf '%d' "$((${failed:-0} + ${passed:-0} + ${skipped:-0} + ${incomplete:-0} + ${snapshot:-0}))"
 }
 
 function bashunit::runner::extract_subshell_type() {
@@ -92,24 +92,21 @@ function bashunit::runner::format_subshell_output() {
 
 function bashunit::runner::detect_runtime_error() {
   local runtime_output=$1
-  local error
-  for error in "command not found" "unbound variable" "permission denied" \
-    "no such file or directory" "syntax error" "bad substitution" \
-    "division by 0" "cannot allocate memory" "bad file descriptor" \
-    "segmentation fault" "illegal option" "argument list too long" \
-    "readonly variable" "missing keyword" "killed" \
-    "cannot execute binary file" "invalid arithmetic operator" \
-    "ambiguous redirect" "integer expression expected" \
-    "too many arguments" "value too great" \
-    "not a valid identifier" "unexpected EOF"; do
-    case "$runtime_output" in
-    *"$error"*)
-      local runtime_error="${runtime_output#*: }"
-      printf '%s' "${runtime_error//$'\n'/}"
-      return 0
-      ;;
-    esac
-  done
+  case "$runtime_output" in
+  *"command not found"* | *"unbound variable"* | *"permission denied"* | \
+    *"no such file or directory"* | *"syntax error"* | *"bad substitution"* | \
+    *"division by 0"* | *"cannot allocate memory"* | *"bad file descriptor"* | \
+    *"segmentation fault"* | *"illegal option"* | *"argument list too long"* | \
+    *"readonly variable"* | *"missing keyword"* | *"killed"* | \
+    *"cannot execute binary file"* | *"invalid arithmetic operator"* | \
+    *"ambiguous redirect"* | *"integer expression expected"* | \
+    *"too many arguments"* | *"value too great"* | \
+    *"not a valid identifier"* | *"unexpected EOF"*)
+    local runtime_error="${runtime_output#*: }"
+    printf '%s' "${runtime_error//$'\n'/}"
+    return 0
+    ;;
+  esac
   printf ''
 }
 
@@ -203,8 +200,8 @@ function bashunit::runner::load_test_files() {
       source_err="$(cat "$source_err_file")"
     fi
     rm -f "$source_err_file"
-    if [ "$source_status" -ne 0 ] || [ "$(printf '%s' "$source_err" \
-      | "$GREP" -cE 'syntax error|unexpected EOF' || true)" -gt 0 ]; then
+    if [ "$source_status" -ne 0 ] || [ "$(printf '%s' "$source_err" |
+      "$GREP" -cE 'syntax error|unexpected EOF' || true)" -gt 0 ]; then
       local message="$source_err"
       [ -z "$message" ] && message="Failed to source '$test_file' (exit $source_status)"
       bashunit::runner::record_file_hook_failure \
diff --git a/tests/unit/runner_test.sh b/tests/unit/runner_test.sh
index 66df4e42..eff156b0 100644
--- a/tests/unit/runner_test.sh
+++ b/tests/unit/runner_test.sh
@@ -47,3 +47,56 @@ function test_extract_assertion_runtime_output_keeps_user_output_that_looks_like
 
   assert_same "✗ Failed: emitted by the code under test" "$actual"
 }
+
+function test_detect_runtime_error_returns_empty_when_input_is_empty() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error "")"
+
+  assert_empty "$actual"
+}
+
+function test_detect_runtime_error_returns_empty_when_no_known_error() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error "all good here")"
+
+  assert_empty "$actual"
+}
+
+function test_detect_runtime_error_matches_command_not_found() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error \
+    "script.sh: line 3: foo: command not found")"
+
+  assert_same "line 3: foo: command not found" "$actual"
+}
+
+function test_detect_runtime_error_matches_syntax_error() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error \
+    "bash: -c: line 1: syntax error near unexpected token")"
+
+  assert_same "-c: line 1: syntax error near unexpected token" "$actual"
+}
+
+function test_detect_runtime_error_matches_killed() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error "process: killed")"
+
+  assert_same "killed" "$actual"
+}
+
+function test_detect_runtime_error_strips_newlines_from_extracted_message() {
+  local input=$'bash: line 1: foo: command not found\nextra'
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error "$input")"
+
+  assert_same "line 1: foo: command not foundextra" "$actual"
+}
+
+function test_detect_runtime_error_matches_unexpected_eof() {
+  local actual
+  actual="$(bashunit::runner::detect_runtime_error \
+    "bash: line 5: unexpected EOF while looking for matching")"
+
+  assert_same "line 5: unexpected EOF while looking for matching" "$actual"
+}