diff --git a/CHANGELOG.md b/CHANGELOG.md
index f9c957b3..2af7b361 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+### Fixed
+- `bashunit upgrade` no longer reports success when the binary download fails; it now exits non-zero, prints the URL it tried, surfaces the underlying curl/wget error, and validates the downloaded file is non-empty before replacing the binary
+
 ### Added
 - `--show-output` displays captured test output on assertion failures (#637)
 - npm registry distribution: `npm install -g bashunit` ships the prebuilt single-file binary (#244)
diff --git a/src/io.sh b/src/io.sh
index c3f2a1e4..a928b37b 100644
--- a/src/io.sh
+++ b/src/io.sh
@@ -21,10 +21,11 @@ function bashunit::io::download_to() {
   local url="$1"
   local output="$2"
   if bashunit::dependencies::has_curl; then
-    curl -L -J -o "$output" "$url" 2>/dev/null
+    curl -fsSL -o "$output" "$url"
   elif bashunit::dependencies::has_wget; then
-    wget -q -O "$output" "$url" 2>/dev/null
+    wget -q -O "$output" "$url"
   else
+    echo "no curl or wget available" >&2
     return 1
   fi
 }
diff --git a/src/upgrade.sh b/src/upgrade.sh
index f65783b4..fd128d2e 100644
--- a/src/upgrade.sh
+++ b/src/upgrade.sh
@@ -1,25 +1,54 @@
 #!/usr/bin/env bash
 
 function bashunit::upgrade::upgrade() {
-  local script_path
-  script_path="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+  local install_dir="${BASHUNIT_INSTALL_DIR:-}"
+  if [ -z "$install_dir" ]; then
+    install_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+  fi
+  local target="$install_dir/bashunit"
+
   local latest_tag
   latest_tag="$(bashunit::helper::get_latest_tag)"
 
+  if [ -z "$latest_tag" ]; then
+    echo "Failed to resolve latest bashunit version. Check your internet connection and that 'git' is installed." >&2
+    return 1
+  fi
+
   if [ "$BASHUNIT_VERSION" = "$latest_tag" ]; then
     echo "> You are already on latest version"
-    return
+    return 0
   fi
 
   echo "> Upgrading bashunit to latest version"
-  cd "$script_path" || exit
 
   local url="https://github.com/TypedDevs/bashunit/releases/download/$latest_tag/bashunit"
-  if ! bashunit::io::download_to "$url" "bashunit"; then
-    echo "Failed to download bashunit"
+  local err_file
+  err_file="$(mktemp 2>/dev/null || echo "/tmp/bashunit_upgrade_err.$$")"
+  local download_status=0
+  bashunit::io::download_to "$url" "$target" 2>"$err_file" || download_status=$?
+
+  if [ "$download_status" -ne 0 ]; then
+    echo "Failed to download bashunit $latest_tag from $url" >&2
+    if [ -s "$err_file" ]; then
+      echo "Reason:" >&2
+      sed 's/^/  /' "$err_file" >&2
+    fi
+    rm -f "$err_file" "$target"
+    return 1
+  fi
+  rm -f "$err_file"
+
+  if [ ! -s "$target" ]; then
+    echo "Failed to download bashunit $latest_tag from $url (empty file)" >&2
+    rm -f "$target"
+    return 1
   fi
 
-  chmod u+x "bashunit"
+  if ! chmod u+x "$target"; then
+    echo "Failed to make $target executable" >&2
+    return 1
+  fi
 
   echo "> bashunit upgraded successfully to latest version $latest_tag"
 }
diff --git a/tests/unit/upgrade_test.sh b/tests/unit/upgrade_test.sh
new file mode 100644
index 00000000..cc5c355a
--- /dev/null
+++ b/tests/unit/upgrade_test.sh
@@ -0,0 +1,118 @@
+#!/usr/bin/env bash
+
+# shellcheck disable=SC2329 # Test functions are invoked indirectly by bashunit
+
+function set_up() {
+  WORK_DIR="$(mktemp -d)"
+  export BASHUNIT_INSTALL_DIR="$WORK_DIR"
+}
+
+function tear_down() {
+  unset BASHUNIT_INSTALL_DIR
+  rm -rf "$WORK_DIR"
+}
+
+function fake_get_latest_tag() {
+  echo "9.9.9"
+}
+
+function fake_get_empty_tag() {
+  echo ""
+}
+
+function fake_download_fail() {
+  echo "curl: (6) Could not resolve host: github.com" >&2
+  return 1
+}
+
+function fake_download_success() {
+  local _url="$1"
+  local output="$2"
+  printf '#!/usr/bin/env bash\necho fake\n' >"$output"
+}
+
+function fake_download_empty() {
+  local _url="$1"
+  local output="$2"
+  : >"$output"
+}
+
+function fake_get_current_tag() {
+  echo "$BASHUNIT_VERSION"
+}
+
+function test_upgrade_aborts_when_download_fails() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_latest_tag
+  bashunit::mock bashunit::io::download_to fake_download_fail
+
+  local output
+  local exit_code=0
+  output="$(bashunit::upgrade::upgrade 2>&1)" || exit_code=$?
+
+  assert_contains "Failed to download bashunit 9.9.9 from" "$output"
+  assert_contains "https://github.com/TypedDevs/bashunit/releases/download/9.9.9/bashunit" "$output"
+  assert_not_contains "upgraded successfully" "$output"
+  assert_equals "1" "$exit_code"
+  assert_file_not_exists "$WORK_DIR/bashunit"
+}
+
+function test_upgrade_surfaces_underlying_download_error_message() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_latest_tag
+  bashunit::mock bashunit::io::download_to fake_download_fail
+
+  local output
+  output="$(bashunit::upgrade::upgrade 2>&1)" || true
+
+  assert_contains "Reason:" "$output"
+  assert_contains "Could not resolve host" "$output"
+}
+
+function test_upgrade_aborts_when_downloaded_file_is_empty() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_latest_tag
+  bashunit::mock bashunit::io::download_to fake_download_empty
+
+  local output
+  local exit_code=0
+  output="$(bashunit::upgrade::upgrade 2>&1)" || exit_code=$?
+
+  assert_contains "empty file" "$output"
+  assert_not_contains "upgraded successfully" "$output"
+  assert_equals "1" "$exit_code"
+  assert_file_not_exists "$WORK_DIR/bashunit"
+}
+
+function test_upgrade_aborts_when_latest_tag_cannot_be_resolved() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_empty_tag
+
+  local output
+  local exit_code=0
+  output="$(bashunit::upgrade::upgrade 2>&1)" || exit_code=$?
+
+  assert_contains "Failed to resolve latest bashunit version" "$output"
+  assert_equals "1" "$exit_code"
+}
+
+function test_upgrade_reports_success_when_download_succeeds() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_latest_tag
+  bashunit::mock bashunit::io::download_to fake_download_success
+
+  local output
+  output="$(bashunit::upgrade::upgrade 2>&1)"
+
+  assert_contains "Upgrading bashunit to latest version" "$output"
+  assert_contains "upgraded successfully to latest version 9.9.9" "$output"
+  assert_not_contains "Failed to download" "$output"
+  assert_file_exists "$WORK_DIR/bashunit"
+  assert_successful_code "$([ -x "$WORK_DIR/bashunit" ] && echo 0 || echo 1)"
+}
+
+function test_upgrade_skips_when_already_on_latest() {
+  bashunit::mock bashunit::helper::get_latest_tag fake_get_current_tag
+
+  local output
+  output="$(bashunit::upgrade::upgrade 2>&1)"
+
+  assert_contains "You are already on latest version" "$output"
+  assert_not_contains "Failed to download" "$output"
+  assert_not_contains "upgraded successfully" "$output"
+}