diff --git a/.travis.yml b/.travis.yml
index 762181b..b396ea9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@ install:
   - chmod +x /tmp/urchin/package/urchin
   - '[ -z "$WITHOUT_CURL" ] || sudo apt-get remove curl -y'
 script:
-  - NVM_DIR=$TRAVIS_BUILD_DIR make TEST_SUITE=$TEST_SUITE URCHIN=/tmp/urchin/package/urchin test-$SHELL
+  - DEBUG='nvm:*' NVM_DIR=$TRAVIS_BUILD_DIR make TEST_SUITE=$TEST_SUITE URCHIN=/tmp/urchin/package/urchin test-$SHELL
 env:
   - SHELL=sh TEST_SUITE=install_script
   - SHELL=dash TEST_SUITE=install_script
diff --git a/install.sh b/install.sh
index 0e22f82..3b3590b 100755
--- a/install.sh
+++ b/install.sh
@@ -1,7 +1,16 @@
 #!/bin/bash
-
 set -e
 
+puts()  (IFS=" "; printf %s\\n "$*" ;)
+error() (IFS=" "; printf %s\\n "$*" >&2 ;)
+debug() (IFS=" "; printf %s\\n ".. $*" >&2 ;)
+
+if [ "$DEBUG" = 'nvm:*' ] || [ "$DEBUG" = 'nvm:install' ]; then
+  NVM_DEBUG=0
+  debug 'Script debugging enabled (in: `install.sh`).'
+fi
+
+
 nvm_has() {
   type "$1" > /dev/null 2>&1
 }
@@ -42,7 +51,9 @@ nvm_source() {
 
 nvm_download() {
   if nvm_has "curl"; then
+    [ "$NVM_DEBUG" = 0 ] && set +x
     curl $*
+    [ "$NVM_DEBUG" = 0 ] && set -x
   elif nvm_has "wget"; then
     # Emulate curl with wget
     ARGS=$(echo "$*" | command sed -e 's/--progress-bar /--progress=bar /' \
@@ -51,7 +62,9 @@ nvm_download() {
                            -e 's/-s /-q /' \
                            -e 's/-o /-O /' \
                            -e 's/-C - /-c /')
+    [ "$NVM_DEBUG" = 0 ] && set +x
     wget $ARGS
+    [ "$NVM_DEBUG" = 0 ] && set +x
   fi
 }
 
@@ -66,10 +79,18 @@ install_nvm_from_git() {
     # Cloning to $NVM_DIR
     echo "=> Downloading nvm from git to '$NVM_DIR'"
     printf "\r=> "
+    [ "$NVM_DEBUG" = 0 ] && set +x
     mkdir -p "$NVM_DIR"
     command git clone "$(nvm_source git)" "$NVM_DIR"
+    [ "$NVM_DEBUG" = 0 ] && set -x
   fi
-  cd "$NVM_DIR" && command git checkout --quiet $(nvm_latest_version) && command git branch --quiet -D master >/dev/null 2>&1
+  
+  [ "$NVM_DEBUG" = 0 ] && set +x
+  cd "$NVM_DIR" || return $?
+  command git checkout --quiet $(nvm_latest_version) || return $?
+  command git branch --quiet -D master >/dev/null 2>&1 || return $?
+  [ "$NVM_DEBUG" = 0 ] && set +x
+  
   return
 }
 
@@ -120,6 +141,57 @@ nvm_detect_profile() {
   fi
 }
 
+#
+# Check whether the user has any globally-installed npm modules in their system
+# Node, and warn them if so.
+#
+nvm_check_global_modules() {
+  command -v npm >/dev/null 2>&1 || return 0
+
+  local NPM_VERSION
+  NPM_VERSION="$(npm --version)"
+  NPM_VERSION="${NPM_VERSION:--1}"
+  [ "$NVM_DEBUG" = 0 ] && debug "NPM detected (at version ${NPM_VERSION}.)"
+  [ "${NPM_VERSION%%[!-0-9]*}" -gt 0 ] || return 0
+
+  local NPM_GLOBAL_MODULES
+  NPM_GLOBAL_MODULES="$(
+    npm list -g --depth=0 |
+    sed '/ npm@/d' |
+    sed '/ (empty)$/d'
+  )"
+
+  local MODULE_COUNT
+  MODULE_COUNT="$(
+    printf %s\\n "$NPM_GLOBAL_MODULES" |
+    sed -ne '1!p' |                             # Remove the first line
+    wc -l | tr -d ' '                           # Count entries
+  )"
+  [ "$NVM_DEBUG" = 0 ] && {
+    debug "(${MODULE_COUNT}) global modules detected:"
+    error "$NPM_GLOBAL_MODULES" ;}
+
+  if [ $MODULE_COUNT -ne 0 ]; then
+    cat <<-'END_MESSAGE'
+	=> You currently have modules installed globally with `npm`. These will no
+	=> longer be linked to the active version of Node when you install a new node
+	=> with `nvm`; and they may (depending on how you construct your `$PATH`)
+	=> override the binaries of modules installed with `nvm`:
+
+	END_MESSAGE
+    printf %s\\n "$NPM_GLOBAL_MODULES"
+    cat <<-'END_MESSAGE'
+
+	=> If you wish to uninstall them at a later point (or re-install them under your
+	=> `nvm` Nodes), you can remove them from the system Node as follows:
+
+	     $ nvm use system
+	     $ npm uninstall -g a_module
+
+	END_MESSAGE
+  fi
+}
+
 nvm_do_install() {
   if [ -z "$METHOD" ]; then
     # Autodetect install method
@@ -169,6 +241,8 @@ nvm_do_install() {
     fi
   fi
 
+  nvm_check_global_modules
+
   echo "=> Close and reopen your terminal to start using nvm"
   nvm_reset
 }
@@ -178,7 +252,11 @@ nvm_do_install() {
 # during the execution of the install script
 #
 nvm_reset() {
-  unset -f nvm_do_install nvm_has nvm_download install_nvm_as_script install_nvm_from_git nvm_reset nvm_detect_profile nvm_latest_version
+  unset -f puts error debug \
+    nvm_reset nvm_has nvm_latest_version \
+    nvm_source nvm_download install_nvm_as_script install_nvm_from_git \
+    nvm_detect_profile nvm_check_global_modules nvm_do_install 
+  unset NPM_DEBUG
 }
 
 [ "_$NVM_ENV" = "_testing" ] || nvm_do_install
diff --git a/test/install_script/nvm_check_global_modules b/test/install_script/nvm_check_global_modules
new file mode 100755
index 0000000..0c6889a
--- /dev/null
+++ b/test/install_script/nvm_check_global_modules
@@ -0,0 +1,87 @@
+#!/bin/sh
+puts() (IFS=" "; printf %s\\n "$*" ;)
+
+cleanup () {
+  rm -rf "$npm_config_prefix/lib" >/dev/null 2>&1
+  unset npm_config_prefix
+
+  rm -f npm
+  PATH="$ORIGINAL_PATH"
+
+  unset -f setup cleanup die
+  unset message ORIGINAL_PATH
+}
+
+die () { puts "!! $@" ; cleanup ; exit 1; }
+
+NVM_ENV=testing . ../../install.sh
+
+setup () {
+  ORIGINAL_PATH="$PATH"
+
+  npm_config_prefix="$(pwd)"
+  export npm_config_prefix
+  mkdir -p "$npm_config_prefix/lib"
+}
+
+setup
+
+
+npm install -g nop >/dev/null || die 'nvm_check_global_modules cannot be tested because `npm` cannot install the `nop` package'
+message=$(nvm_check_global_modules)
+[ ! -z "$message" ] || {
+  puts '-- `npm --version`: '"$(npm --version)"
+  puts '-- `npm list -g`:'
+  npm list -g --depth=0
+  puts '-- Printed message:'
+  puts "'''$message'''"
+
+  die "nvm_check_global_modules should have printed a notice when npm had global modules installed" ;}
+
+
+npm uninstall -g nop >/dev/null
+message=$(nvm_check_global_modules)
+[ -z "$message" ] || {
+  puts '-- `npm --version`: '"$(npm --version)"
+  puts '-- `npm list -g`:'
+  npm list -g --depth=0
+  puts '-- Printed message:'
+  puts "'''$message'''"
+
+  die "nvm_check_global_modules should not have printed a notice when npm had no global modules installed" ;}
+
+
+# Faking an installation of npm
+mkdir -p "$npm_config_prefix/lib/node_modules/npm"
+cat <<'JSON' >"$npm_config_prefix/lib/node_modules/npm/package.json"
+{ "name": "npm", "version": "0.0.1fake" }
+JSON
+
+message=$(nvm_check_global_modules)
+[ -z "$message" ] || {
+  puts '-- `which npm`: '     "$(which npm)"
+  puts '-- `npm --version`: ' "$(npm --version)"
+  puts '-- `npm list -g`:'
+  npm list -g --depth=0
+  puts '-- Printed message:'
+  puts "'''$message'''"
+
+  die "nvm_check_global_modules should not have printed a notice when npm had only itself installed as a global module" ;}
+
+
+# Faking the absence of npm
+PATH=".:$PATH"
+touch npm
+chmod +x npm
+
+message=$(nvm_check_global_modules)
+[ -z "$message" ] || {
+  puts '-- `which npm`: '     "$(which npm)"
+  puts '-- `npm --version`: ' "$(npm --version)"
+  puts '-- Printed message:'
+  puts "'''$message'''"
+
+  die "nvm_check_global_modules should not have printed a notice when npm was unavailable" ;}
+
+
+cleanup