diff --git a/CHANGELOG.md b/CHANGELOG.md
index e91de2a1..e6f1075a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,7 +3,10 @@
 ## Unreleased
 
 ### Changed
-- A `--tag` that matches nothing names the tags the run saw, or says no test carries one. Tags appear only in `# @tag` comments and nothing lists them, so a typo had no way back (#1265)
+- A `--tag` matching nothing now names the tags the run saw, or says no test carries one — tags live only in `# @tag` comments and nothing lists them, so a typo had no way back (#1265)
+
+### Fixed
+- A test that both fails an assertion and hits a shell error no longer reports the failure text with the diagnostic glued onto the end; the error message is the diagnostic alone (#1267)
 
 ## [0.48.0](https://github.com/TypedDevs/bashunit/compare/0.47.0...0.48.0) - 2026-08-14
 
diff --git a/src/runner/diagnostics.sh b/src/runner/diagnostics.sh
index 1c3c09a8..b7d9e5f1 100644
--- a/src/runner/diagnostics.sh
+++ b/src/runner/diagnostics.sh
@@ -50,11 +50,13 @@ function bashunit::runner::_scan_diagnostic_lines() {
       *"ambiguous redirect"* | *"integer expression expected"* | \
       *"too many arguments"* | *"value too great"* | \
       *"not a valid identifier"* | *"unexpected EOF"*)
-      # Extract from the whole capture, not the matched line: the message shape
-      # (leading source stripped, newlines removed) is pinned by
-      # tests/unit/runner/diagnostics_test.sh.
-      local runtime_error="${runtime_output#*: }"
-      _BASHUNIT_RUNNER_RUNTIME_ERROR_OUT="${runtime_error//$'\n'/}"
+      # Extract from the matched line, not the whole capture. A test can both
+      # fail an assertion and hit a runtime error, and bashunit renders the
+      # failure inside the capture subshell -- so its own "✗ Failed: <name>"
+      # text sits ahead of the shell's diagnostic. Stripping to the first ": "
+      # across the whole blob landed inside that rendering and reported the
+      # failure text with the diagnostic glued onto the end.
+      _BASHUNIT_RUNNER_RUNTIME_ERROR_OUT="${line#*: }"
       return
       ;;
     esac
diff --git a/tests/acceptance/bashunit_runtime_error_classification_test.sh b/tests/acceptance/bashunit_runtime_error_classification_test.sh
index a14529c6..f0ecb8ed 100644
--- a/tests/acceptance/bashunit_runtime_error_classification_test.sh
+++ b/tests/acceptance/bashunit_runtime_error_classification_test.sh
@@ -34,3 +34,20 @@ function test_a_real_shell_error_is_still_reported() {
   assert_contains "✗ Error: Hits a real shell error" "$output"
   assert_contains "command not found" "$output"
 }
+
+# A test can fail an assertion *and* hit a shell error. The reported error must
+# be the diagnostic alone: extracting it from the whole capture stripped to the
+# first ": " anywhere, which landed inside bashunit's own "✗ Failed: <name>"
+# rendering, so the error read as the failure text with the diagnostic glued on
+# ("...but got 'b' at file:2file: line 8: nope: command not found").
+function test_an_assertion_failure_does_not_leak_into_the_error_message() {
+  local fixture=tests/acceptance/fixtures/runtime_error/fails_and_errors.sh
+  local output exit_code=0
+
+  output=$(LC_ALL=C NO_COLOR=1 ./bashunit --no-parallel --skip-env-file "$fixture" 2>&1) || exit_code=$?
+
+  assert_same 1 "$exit_code"
+  assert_contains "line 8: no_such_command_from_a_fixture: command not found" "$output"
+  # The failure text must not appear inside the error message line.
+  assert_not_contains "but got  'b'    at" "$output"
+}
diff --git a/tests/acceptance/fixtures/runtime_error/fails_and_errors.sh b/tests/acceptance/fixtures/runtime_error/fails_and_errors.sh
new file mode 100644
index 00000000..4f0f7dcf
--- /dev/null
+++ b/tests/acceptance/fixtures/runtime_error/fails_and_errors.sh
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+# Both at once: the assertion fails, then the shell cannot find the command.
+# bashunit renders the failure inside the capture subshell, so its own text
+# precedes the diagnostic in the captured output.
+function test_fails_an_assertion_and_then_hits_a_shell_error() {
+  assert_same "a" "b"
+  no_such_command_from_a_fixture
+}
diff --git a/tests/unit/runner/diagnostics_test.sh b/tests/unit/runner/diagnostics_test.sh
index ff5626a1..745de9f3 100644
--- a/tests/unit/runner/diagnostics_test.sh
+++ b/tests/unit/runner/diagnostics_test.sh
@@ -30,11 +30,17 @@ function test_detect_runtime_error_matches_killed() {
   assert_same "killed" "$_BASHUNIT_RUNNER_RUNTIME_ERROR_OUT"
 }
 
-function test_detect_runtime_error_strips_newlines_from_extracted_message() {
+# The message is one line because it is *one line of the capture* -- the
+# diagnostic itself, with its source prefix stripped. It used to be the whole
+# capture with the newlines deleted, which glued unrelated output onto the end
+# ("...command not foundextra"). Anything else the test printed is display
+# output, and stays there.
+function test_detect_runtime_error_reports_the_diagnostic_line_not_the_whole_capture() {
   local input=$'bash: line 1: foo: command not found\nextra'
   bashunit::runner::detect_runtime_error "$input"
 
-  assert_same "line 1: foo: command not foundextra" "$_BASHUNIT_RUNNER_RUNTIME_ERROR_OUT"
+  assert_same "line 1: foo: command not found" "$_BASHUNIT_RUNNER_RUNTIME_ERROR_OUT"
+  assert_same "$input" "$_BASHUNIT_RUNNER_RUNTIME_OUTPUT_OUT"
 }
 
 function test_detect_runtime_error_matches_unexpected_eof() {
@@ -122,3 +128,20 @@ function test_detect_runtime_error_prefers_the_matched_text_over_the_exit_code()
 
   assert_contains "command not found" "$_BASHUNIT_RUNNER_RUNTIME_ERROR_OUT"
 }
+
+# A test can both fail an assertion and hit a runtime error. bashunit prints the
+# failure inside the capture subshell, so its own rendering sits in the capture
+# ahead of the shell's diagnostic. Extracting from the whole capture then strips
+# to the first ": " anywhere -- which lands inside "✗ Failed: <name>" -- and the
+# reported error becomes the failure text with the diagnostic glued on the end.
+function test_detect_runtime_error_reports_only_the_diagnostic_not_the_captured_failure() {
+  local input="✗ Failed: Both
+    Expected 'a'
+    but got  'b'
+    at f_test.sh:2
+f_test.sh: line 4: nope: command not found"
+
+  bashunit::runner::detect_runtime_error "$input"
+
+  assert_same "line 4: nope: command not found" "$_BASHUNIT_RUNNER_RUNTIME_ERROR_OUT"
+}