diff --git a/nvm.sh b/nvm.sh
index 0a9b586..24ff367 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -13,7 +13,8 @@ nvm_has() {
 }
 
 nvm_is_alias() {
-  command alias "$1" > /dev/null 2>&1
+  # this is intentionally not "command alias" so it works in zsh.
+  \alias "$1" > /dev/null 2>&1
 }
 
 nvm_get_latest() {
diff --git a/test/fast/Unit tests/nvm_is_alias b/test/fast/Unit tests/nvm_is_alias
new file mode 100755
index 0000000..b5cf305
--- /dev/null
+++ b/test/fast/Unit tests/nvm_is_alias	
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+cleanup () { unalias foo; unalias grep; }
+die () { echo $@ ; cleanup ; exit 1; }
+
+. ../../../nvm.sh
+
+alias foo='bar'
+nvm_is_alias foo || die '"nvm_is_alias foo" was not true'
+
+! nvm_is_alias nvm_is_alias || die '"nvm_is_alias nvm_is_alias was not false'
+
+alias grep='grep'
+unalias grep || die '"unalias grep" failed'
+! nvm_is_alias grep || die '"nvm_is_alias grep" with unaliased grep was not false'
+
+alias grep='grep'
+nvm_is_alias grep || die '"nvm_is_alias grep" with aliased grep was not true'
+
+cleanup