diff --git a/algs4/Makefile b/algs4/Makefile
index 7df9fa2..fa5000b 100644
--- a/algs4/Makefile
+++ b/algs4/Makefile
@@ -1,6 +1,8 @@
 CLEAN_GOPATH := $(shell echo $(GOPATH) | tr ":" "\n" | grep -v '^$$' | grep -v $(PWD) | tr "\n" ":")
 GOPATH := $(PWD):$(CLEAN_GOPATH)
-PACKAGES := meatballhat.com/algs4-gcd
+PACKAGES := \
+	meatballhat.com/algs4 \
+	meatballhat.com/algs4-gcd
 
 test: build
 	go test $(PACKAGES)
diff --git a/algs4/src/meatballhat.com/algs4-gcd/main.go b/algs4/src/meatballhat.com/algs4-gcd/main.go
index c7fa5f1..a2a7223 100644
--- a/algs4/src/meatballhat.com/algs4-gcd/main.go
+++ b/algs4/src/meatballhat.com/algs4-gcd/main.go
@@ -6,15 +6,11 @@ import (
 	"strconv"
 )
 
-const USAGE string = `Usage: algs4-gcd <int> <int>`
+import (
+	"meatballhat.com/algs4"
+)
 
-func gcd(p, q uint64) uint64 {
-	if q == 0 {
-		return p
-	}
-	r := p % q
-	return gcd(q, r)
-}
+const USAGE string = `Usage: algs4-gcd <uint> <uint>`
 
 func main() {
 	if len(os.Args) < 3 {
@@ -34,5 +30,5 @@ func main() {
 		os.Exit(1)
 	}
 
-	fmt.Println(gcd(p, q))
+	fmt.Println(algs4.Gcd(p, q))
 }
diff --git a/algs4/src/meatballhat.com/algs4/gcd.go b/algs4/src/meatballhat.com/algs4/gcd.go
new file mode 100644
index 0000000..0a06355
--- /dev/null
+++ b/algs4/src/meatballhat.com/algs4/gcd.go
@@ -0,0 +1,9 @@
+package algs4
+
+func Gcd(p, q uint64) uint64 {
+	if q == 0 {
+		return p
+	}
+	r := p % q
+	return Gcd(q, r)
+}
diff --git a/algs4/src/meatballhat.com/algs4/gcd_test.go b/algs4/src/meatballhat.com/algs4/gcd_test.go
new file mode 100644
index 0000000..0ae6c38
--- /dev/null
+++ b/algs4/src/meatballhat.com/algs4/gcd_test.go
@@ -0,0 +1,16 @@
+package algs4_test
+
+import (
+	"testing"
+)
+
+import (
+	"meatballhat.com/algs4"
+)
+
+func TestGcd(t *testing.T) {
+	d := algs4.Gcd(uint64(81), uint64(72))
+	if d != 9 {
+		t.Error("WRONG")
+	}
+}