diff --git a/bin/rbenv-install b/bin/rbenv-install
index 9bb6c108..543b709b 100755
--- a/bin/rbenv-install
+++ b/bin/rbenv-install
@@ -96,11 +96,13 @@ for option in "${OPTIONS[@]}"; do
     exec ruby-build --version
     ;;
   * )
-    usage 1
+    usage 1 >&2
     ;;
   esac
 done
 
+[ "${#ARGUMENTS[@]}" -le 1 ] || usage 1 >&2
+
 unset VERSION_NAME
 
 # The first argument contains the definition to install. If the
@@ -109,8 +111,7 @@ unset VERSION_NAME
 # version is not specified.
 DEFINITION="${ARGUMENTS[0]}"
 [ -n "$DEFINITION" ] || DEFINITION="$(rbenv-local 2>/dev/null || true)"
-[ -n "$DEFINITION" ] || usage 1
-
+[ -n "$DEFINITION" ] || usage 1 >&2
 
 # Define `before_install` and `after_install` functions that allow
 # plugin hooks to register a string of code for execution before or
diff --git a/bin/rbenv-uninstall b/bin/rbenv-uninstall
index 10aa6e93..ea65c45a 100755
--- a/bin/rbenv-uninstall
+++ b/bin/rbenv-uninstall
@@ -17,24 +17,32 @@ if [ "$1" = "--complete" ]; then
   exec rbenv versions --bare
 fi
 
+usage() {
+  # We can remove the sed fallback once rbenv 0.4.0 is widely available.
+  rbenv-help uninstall 2>/dev/null || sed -ne '/^#/!q;s/.//;s/.//;1,4d;p' < "$0"
+  [ -z "$1" ] || exit "$1"
+}
+
 if [ -z "$RBENV_ROOT" ]; then
   RBENV_ROOT="${HOME}/.rbenv"
 fi
 
+if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
+  usage 0
+fi
+
 unset FORCE
 if [ "$1" = "-f" ] || [ "$1" = "--force" ]; then
   FORCE=true
   shift
 fi
 
+[ "$#" -eq 1 ] || usage 1 >&2
+
 DEFINITION="$1"
 case "$DEFINITION" in
 "" | -* )
-  # We can remove the sed fallback once rbenv 0.4.0 is widely available.
-  { rbenv-help uninstall 2>/dev/null ||
-    sed -ne '/^#/!q;s/.\{1,2\}//;1,4d;p' < "$0"
-  } >&2
-  exit 1
+  usage 1 >&2
   ;;
 esac
 
diff --git a/bin/ruby-build b/bin/ruby-build
index 64a750a2..54a31406 100755
--- a/bin/ruby-build
+++ b/bin/ruby-build
@@ -1,4 +1,13 @@
 #!/usr/bin/env bash
+#
+# Usage: ruby-build [-kvp] <definition> <prefix>
+#        ruby-build --definitions
+#
+#   -k/--keep        Do not remove source tree after installation
+#   -v/--verbose     Verbose mode: print compilation status to stdout
+#   -p/--patch       Apply a patch from stdin before building
+#   --definitions    List all built-in definitions
+#
 
 RUBY_BUILD_VERSION="20141113"
 
@@ -954,14 +963,8 @@ version() {
 }
 
 usage() {
-  { version
-    echo "usage: ruby-build [-k|--keep] [-v|--verbose] [-p|--patch] definition prefix"
-    echo "       ruby-build --definitions"
-  } >&2
-
-  if [ -z "$1" ]; then
-    exit 1
-  fi
+  sed -ne '/^#/!q;s/.\{1,2\}//;1,2d;p' < "$0"
+  [ -z "$1" ] || exit "$1"
 }
 
 list_definitions() {
@@ -992,15 +995,9 @@ parse_options "$@"
 for option in "${OPTIONS[@]}"; do
   case "$option" in
   "h" | "help" )
-    usage without_exiting
-    { echo
-      echo "  -k/--keep        Do not remove source tree after installation"
-      echo "  -v/--verbose     Verbose mode: print compilation status to stdout"
-      echo "  -p/--patch       Apply a patch from stdin before building"
-      echo "  --definitions    List all built-in definitions"
-      echo
-    } >&2
-    exit 0
+    version
+    echo
+    usage 0
     ;;
   "definitions" )
     list_definitions
@@ -1022,9 +1019,11 @@ for option in "${OPTIONS[@]}"; do
   esac
 done
 
+[ "${#ARGUMENTS[@]}" -eq 2 ] || usage 1 >&2
+
 DEFINITION_PATH="${ARGUMENTS[0]}"
 if [ -z "$DEFINITION_PATH" ]; then
-  usage
+  usage 1 >&2
 elif [ ! -f "$DEFINITION_PATH" ]; then
   for DEFINITION_DIR in "${RUBY_BUILD_DEFINITIONS[@]}"; do
     if [ -f "${DEFINITION_DIR}/${DEFINITION_PATH}" ]; then
@@ -1041,7 +1040,7 @@ fi
 
 PREFIX_PATH="${ARGUMENTS[1]}"
 if [ -z "$PREFIX_PATH" ]; then
-  usage
+  usage 1 >&2
 elif [ "${PREFIX_PATH#/}" = "$PREFIX_PATH" ]; then
   PREFIX_PATH="${PWD}/${PREFIX_PATH}"
 fi
diff --git a/test/arguments.bats b/test/arguments.bats
new file mode 100644
index 00000000..77eb91cf
--- /dev/null
+++ b/test/arguments.bats
@@ -0,0 +1,23 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+@test "not enought arguments for ruby-build" {
+  # use empty inline definition so nothing gets built anyway
+  local definition="${TMP}/build-definition"
+  echo '' > "$definition"
+
+  run ruby-build "$definition"
+  assert_failure
+  assert_output_contains 'Usage: ruby-build'
+}
+
+@test "extra arguments for ruby-build" {
+  # use empty inline definition so nothing gets built anyway
+  local definition="${TMP}/build-definition"
+  echo '' > "$definition"
+
+  run ruby-build "$definition" "${TMP}/install" ""
+  assert_failure
+  assert_output_contains 'Usage: ruby-build'
+}
diff --git a/test/rbenv.bats b/test/rbenv.bats
index dc189f07..b51ed167 100644
--- a/test/rbenv.bats
+++ b/test/rbenv.bats
@@ -146,3 +146,42 @@ ${RBENV_ROOT}/plugins/bar/share/ruby-build
 ${RBENV_ROOT}/plugins/foo/share/ruby-build
 OUT
 }
+
+@test "not enough arguments for rbenv-install" {
+  stub_ruby_build
+  run rbenv-install
+  assert_failure
+  assert_output_contains 'Usage: rbenv install'
+}
+
+@test "too many arguments for rbenv-install" {
+  stub_ruby_build
+  run rbenv-install 2.1.1 2.1.2
+  assert_failure
+  assert_output_contains 'Usage: rbenv install'
+}
+
+@test "show help for rbenv-install" {
+  stub_ruby_build
+  run rbenv-install -h
+  assert_success
+  assert_output_contains 'Usage: rbenv install'
+}
+
+@test "not enough arguments rbenv-uninstall" {
+  run rbenv-uninstall
+  assert_failure
+  assert_output_contains 'Usage: rbenv uninstall'
+}
+
+@test "too many arguments for rbenv-uninstall" {
+  run rbenv-uninstall 2.1.1 2.1.2
+  assert_failure
+  assert_output_contains 'Usage: rbenv uninstall'
+}
+
+@test "show help for rbenv-uninstall" {
+  run rbenv-uninstall -h
+  assert_success
+  assert_output_contains 'Usage: rbenv uninstall'
+}