diff --git a/nvm.sh b/nvm.sh
index 01585e3..7f734fe 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -284,12 +284,12 @@ nvm_ls_remote() {
 }
 
 nvm_checksum() {
-  if nvm_has "shasum"; then
-    checksum=$(shasum $1 | \awk '{print $1}')
+  if nvm_has "sha1sum"; then
+    checksum=$(sha1sum $1 | \awk '{print $1}')
   elif nvm_has "sha1"; then
     checksum=$(sha1 -q $1)
   else
-    checksum=$(sha1sum $1 | \awk '{print $1}')
+    checksum=$(shasum $1 | \awk '{print $1}')
   fi
 
   if [ "$checksum" = "$2" ]; then
diff --git a/test/fast/Unit tests/nvm_checksum b/test/fast/Unit tests/nvm_checksum
new file mode 100755
index 0000000..73cf1f1
--- /dev/null
+++ b/test/fast/Unit tests/nvm_checksum	
@@ -0,0 +1,18 @@
+#!/bin/sh
+
+cleanup () {
+  rm tmp/emptyfile tmp/testfile
+  rmdir tmp
+}
+die () { echo $@ ; cleanup; exit 1; }
+
+. ../../../nvm.sh
+
+mkdir -p tmp
+touch tmp/emptyfile
+echo -n "test" > tmp/testfile
+
+nvm_checksum tmp/emptyfile "da39a3ee5e6b4b0d3255bfef95601890afd80709" || die "nvm_checksum on an empty file did not match the SHA1 digest of the empty string"
+nvm_checksum tmp/testfile "da39a3ee5e6b4b0d3255bfef95601890afd80709" && die "nvm_checksum allowed a bad checksum"
+
+cleanup