diff --git a/CHANGELOG.md b/CHANGELOG.md
index 33fffd7e..c501dee8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,8 @@
 - The `--parallel` unsupported-OS warning no longer claims Alpine is excluded
 
 ### Fixed
+- A configured external git differ (`diff.external` / `GIT_EXTERNAL_DIFF`, e.g. difftastic) no longer blanks the multiline and snapshot failure diffs, which now render with `--no-ext-diff` (#912)
+- Time reads and the JUnit report no longer set the locale with a temporary-environment prefix (`LC_ALL=C cmd`), which segfaults inside a command substitution on Bash 5.3.9 macOS (#912)
 - Call assertions (`assert_not_called`, `assert_have_been_called*`) fail with `was never registered as a spy` instead of reporting zero calls when the name was never spied — a typo used to pass silently (#895)
 - The per-argument form a spy records was written with a literal `$'\x1f'` separator instead of the byte, so it could not be compared against (#894)
 - `--parallel` no longer discards worker stderr written outside a test body; it renders as a `Stderr from <file>` block (#864)
diff --git a/src/clock.sh b/src/clock.sh
index 035cb66e..124c31a1 100644
--- a/src/clock.sh
+++ b/src/clock.sh
@@ -182,7 +182,10 @@ function bashunit::clock::now() {
 
 function bashunit::clock::shell_time() {
   # Get time directly from the shell variable EPOCHREALTIME (Bash 5+)
-  [ -n "${EPOCHREALTIME+x}" ] && [ -n "$EPOCHREALTIME" ] && LC_ALL=C echo "$EPOCHREALTIME"
+  # No `LC_ALL=C` prefix: the value is expanded before the temporary environment
+  # applies, so it cannot normalize the decimal separator (callers accept both),
+  # and that form segfaults inside `$()` on Bash 5.3 macOS (#912).
+  [ -n "${EPOCHREALTIME+x}" ] && [ -n "$EPOCHREALTIME" ] && echo "$EPOCHREALTIME"
 }
 
 function bashunit::clock::total_runtime_in_milliseconds() {
diff --git a/src/console_results.sh b/src/console_results.sh
index 882baf09..a17a6bf3 100644
--- a/src/console_results.sh
+++ b/src/console_results.sh
@@ -312,8 +312,9 @@ function bashunit::console_results::render_diff() {
 
   # `git diff` exits non-zero when the files differ; the `|| true` keeps that
   # from tripping `set -e`/`pipefail` under --strict. `tail -n +6` drops git's
-  # header lines; `sed` indents the body.
-  git diff --no-index --word-diff "$color_flag" \
+  # header lines; `sed` indents the body. `--no-ext-diff` ignores a user's
+  # `diff.external`/`GIT_EXTERNAL_DIFF`, which would replace this word-diff.
+  git diff --no-index --no-ext-diff --word-diff "$color_flag" \
     "$expected_file" "$actual_file" 2>/dev/null |
     tail -n +6 | sed "s/^/    /" || true
 }
diff --git a/src/reports.sh b/src/reports.sh
index dcbddc40..b3e1df45 100755
--- a/src/reports.sh
+++ b/src/reports.sh
@@ -102,7 +102,9 @@ function bashunit::reports::generate_junit_xml() {
   local tests_failed=$(bashunit::state::get_tests_failed)
   local time_ms=$(bashunit::clock::total_runtime_in_milliseconds)
   local time
-  time=$(LC_ALL=C awk -v ms="$time_ms" 'BEGIN {printf "%.3f", ms/1000}')
+  # `env` rather than a bare `LC_ALL=C` prefix: C keeps awk's radix a dot for the
+  # XML, and that prefix form segfaults inside `$()` on Bash 5.3 macOS (#912).
+  time=$(env LC_ALL=C awk -v ms="$time_ms" 'BEGIN {printf "%.3f", ms/1000}')
 
   {
     echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
@@ -120,7 +122,7 @@ function bashunit::reports::generate_junit_xml() {
       local test_time_ms="${_BASHUNIT_REPORTS_TEST_DURATIONS[$i]:-}"
       local failure_message="${_BASHUNIT_REPORTS_TEST_FAILURES[$i]:-}"
       local test_time
-      test_time=$(LC_ALL=C awk -v ms="$test_time_ms" 'BEGIN {printf "%.3f", ms/1000}')
+      test_time=$(env LC_ALL=C awk -v ms="$test_time_ms" 'BEGIN {printf "%.3f", ms/1000}')
 
       echo "    <testcase file=\"$file\""
       echo "        name=\"$name\""
diff --git a/tests/acceptance/bashunit_init_test.sh b/tests/acceptance/bashunit_init_test.sh
index 927486b5..b792737a 100644
--- a/tests/acceptance/bashunit_init_test.sh
+++ b/tests/acceptance/bashunit_init_test.sh
@@ -15,7 +15,7 @@ function tear_down() {
 
 function test_bashunit_init_creates_structure() {
   pushd "$TMP_DIR" >/dev/null
-  "$BASHUNIT_PATH" init >/tmp/init.log
+  "$BASHUNIT_PATH" init >"$TMP_DIR/init.log"
   assert_file_exists "tests/example_test.sh"
   assert_file_exists "tests/bootstrap.sh"
   popd >/dev/null
@@ -23,7 +23,7 @@ function test_bashunit_init_creates_structure() {
 
 function test_bashunit_init_custom_directory() {
   pushd "$TMP_DIR" >/dev/null
-  "$BASHUNIT_PATH" init custom >/tmp/init.log
+  "$BASHUNIT_PATH" init custom >"$TMP_DIR/init.log"
   assert_file_exists "custom/example_test.sh"
   assert_file_exists "custom/bootstrap.sh"
   popd >/dev/null
@@ -31,7 +31,7 @@ function test_bashunit_init_custom_directory() {
 
 function test_bashunit_init_creates_github_workflow() {
   pushd "$TMP_DIR" >/dev/null
-  "$BASHUNIT_PATH" init >/tmp/init.log
+  "$BASHUNIT_PATH" init >"$TMP_DIR/init.log"
   assert_file_exists ".github/workflows/tests.yml"
   assert_file_contains ".github/workflows/tests.yml" "TypedDevs/bashunit@"
   popd >/dev/null
@@ -41,7 +41,7 @@ function test_bashunit_init_does_not_overwrite_existing_workflow() {
   pushd "$TMP_DIR" >/dev/null
   mkdir -p ".github/workflows"
   echo "custom-workflow" >".github/workflows/tests.yml"
-  "$BASHUNIT_PATH" init >/tmp/init.log
+  "$BASHUNIT_PATH" init >"$TMP_DIR/init.log"
   assert_file_contains ".github/workflows/tests.yml" "custom-workflow"
   popd >/dev/null
 }
@@ -51,7 +51,7 @@ function test_bashunit_init_updates_env() {
 
   pushd "$TMP_DIR" >/dev/null
   echo "BASHUNIT_BOOTSTRAP=old/bootstrap.sh" >.env
-  "$BASHUNIT_PATH" init custom >/tmp/init.log
+  "$BASHUNIT_PATH" init custom >"$TMP_DIR/init.log"
   assert_file_exists "custom/example_test.sh"
   assert_file_exists "custom/bootstrap.sh"
   assert_file_contains .env "#BASHUNIT_BOOTSTRAP=old/bootstrap.sh"
diff --git a/tests/acceptance/bashunit_syntax_error_test.sh b/tests/acceptance/bashunit_syntax_error_test.sh
index 2f0a1f1e..7cc5476a 100644
--- a/tests/acceptance/bashunit_syntax_error_test.sh
+++ b/tests/acceptance/bashunit_syntax_error_test.sh
@@ -10,7 +10,7 @@ function test_bashunit_when_test_file_has_syntax_error() {
 
   local actual_raw
   set +e
-  actual_raw="$(LC_ALL=C LANG=C ./bashunit \
+  actual_raw="$(./bashunit \
     --no-parallel --detailed --env "$TEST_ENV_FILE" "$test_file" 2>&1)"
   set -e
 
@@ -19,6 +19,6 @@ function test_bashunit_when_test_file_has_syntax_error() {
 
   assert_contains "failed" "$actual"
   assert_contains "Error" "$actual"
-  assert_general_error "$(LC_ALL=C LANG=C ./bashunit \
+  assert_general_error "$(./bashunit \
     --no-parallel --env "$TEST_ENV_FILE" "$test_file" 2>&1)"
 }
diff --git a/tests/unit/bash_compatibility_test.sh b/tests/unit/bash_compatibility_test.sh
index 1faeee99..454cf4c1 100644
--- a/tests/unit/bash_compatibility_test.sh
+++ b/tests/unit/bash_compatibility_test.sh
@@ -102,3 +102,14 @@ function test_src_has_no_coproc() {
 function test_src_has_no_parameter_transformations() {
   assert_empty "$(bashunit::compat::offenders '\$\{[A-Za-z_][A-Za-z0-9_]*@[QEPAKa]\}')"
 }
+
+# A temporary-environment locale prefix (`LC_ALL=C cmd`) makes bash change its
+# own locale for that command. Bash 5.3.9 on macOS segfaults on that form inside
+# a command substitution -- `x=$(LC_ALL=C echo hi)` exits 139 (#912) -- and no CI
+# job runs that build. Use `env LC_ALL=C cmd` instead, which passes the locale
+# straight to the child and never touches bash's own.
+function test_src_has_no_temporary_locale_assignment_prefix() {
+  local pattern='(^|[;&|(])[[:space:]]*((LC_[A-Z_]+|LANG)=[^[:space:]]*[[:space:]]+)+[^[:space:]=]'
+
+  assert_empty "$(bashunit::compat::offenders "$pattern")"
+}
diff --git a/tests/unit/console_results_diff_test.sh b/tests/unit/console_results_diff_test.sh
index b8500cd4..c4110bca 100644
--- a/tests/unit/console_results_diff_test.sh
+++ b/tests/unit/console_results_diff_test.sh
@@ -62,3 +62,26 @@ function test_render_diff_shows_changed_tokens_without_color() {
   rm -f "$a" "$b"
   unset BASHUNIT_NO_COLOR
 }
+
+function test_render_diff_ignores_a_configured_external_diff() {
+  if ! bashunit::dependencies::has_git; then
+    bashunit::skip "git not available" && return
+  fi
+  export BASHUNIT_NO_COLOR=true
+  # An external differ (difftastic in #912) replaces git's own output, so without
+  # --no-ext-diff the rendered diff is whatever it prints -- here nothing at all.
+  export GIT_EXTERNAL_DIFF=true
+  local a b
+  a=$(bashunit::temp_file diff_a)
+  b=$(bashunit::temp_file diff_b)
+  printf 'alpha\nbeta\ngamma\n' >"$a"
+  printf 'alpha\nDELTA\ngamma\n' >"$b"
+
+  local output
+  output=$(bashunit::console_results::render_diff "$a" "$b")
+
+  assert_contains "beta" "$output"
+  assert_contains "DELTA" "$output"
+  rm -f "$a" "$b"
+  unset BASHUNIT_NO_COLOR GIT_EXTERNAL_DIFF
+}
diff --git a/tests/unit/console_results_test.sh b/tests/unit/console_results_test.sh
index 4bc7e7d1..5e69e24c 100644
--- a/tests/unit/console_results_test.sh
+++ b/tests/unit/console_results_test.sh
@@ -363,6 +363,7 @@ function test_render_execution_time_on_osx_with_perl() {
 
   local render_result
   mock_macos
+  _BASHUNIT_CLOCK_NOW_IMPL="perl"
   bashunit::mock bashunit::dependencies::has_perl mock_true
   _BASHUNIT_START_TIME="1726393394574382186"
   bashunit::mock perl <<<"1726393394574372186"