diff --git a/go.mod b/go.mod
index c3f3e81e..a9fbb0c9 100644
--- a/go.mod
+++ b/go.mod
@@ -2,7 +2,4 @@ module github.com/evanw/esbuild
 
 go 1.13
 
-require (
-	github.com/kylelemons/godebug v1.1.0
-	golang.org/x/sys v0.0.0-20200501145240-bc7a7d42d5c3
-)
+require golang.org/x/sys v0.0.0-20200501145240-bc7a7d42d5c3
diff --git a/go.sum b/go.sum
index 9be20ecc..2feba761 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,2 @@
-github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
-github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 golang.org/x/sys v0.0.0-20200501145240-bc7a7d42d5c3 h1:5B6i6EAiSYyejWfvc5Rc9BbI3rzIsrrXfAQBWnYfn+w=
 golang.org/x/sys v0.0.0-20200501145240-bc7a7d42d5c3/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
diff --git a/internal/bundler/bundler_test.go b/internal/bundler/bundler_test.go
index 1387dc98..1dd7607d 100644
--- a/internal/bundler/bundler_test.go
+++ b/internal/bundler/bundler_test.go
@@ -21,7 +21,7 @@ import (
 	"github.com/evanw/esbuild/internal/fs"
 	"github.com/evanw/esbuild/internal/logger"
 	"github.com/evanw/esbuild/internal/resolver"
-	"github.com/kylelemons/godebug/diff"
+	"github.com/evanw/esbuild/internal/test"
 )
 
 func es(version int) compat.JSFeature {
@@ -36,7 +36,7 @@ func assertEqual(t *testing.T, a interface{}, b interface{}) {
 		stringA := fmt.Sprintf("%v", a)
 		stringB := fmt.Sprintf("%v", b)
 		if strings.Contains(stringA, "\n") {
-			t.Fatal(diff.Diff(stringB, stringA))
+			t.Fatal(test.Diff(stringB, stringA))
 		} else {
 			t.Fatalf("%s != %s", a, b)
 		}
diff --git a/internal/test/diff.go b/internal/test/diff.go
new file mode 100644
index 00000000..17d28d37
--- /dev/null
+++ b/internal/test/diff.go
@@ -0,0 +1,66 @@
+package test
+
+import (
+	"strings"
+)
+
+func Diff(old string, new string) string {
+	return strings.Join(diffRec(nil, strings.Split(old, "\n"), strings.Split(new, "\n")), "\n")
+}
+
+// This is a simple recursive line-by-line diff implementation
+func diffRec(result []string, old []string, new []string) []string {
+	o, n, common := lcSubstr(old, new)
+
+	if common == 0 {
+		// Everything changed
+		for _, line := range old {
+			result = append(result, "-"+line)
+		}
+		for _, line := range new {
+			result = append(result, "+"+line)
+		}
+	} else {
+		// Something in the middle stayed the same
+		result = diffRec(result, old[:o], new[:n])
+		for _, line := range old[o : o+common] {
+			result = append(result, " "+line)
+		}
+		result = diffRec(result, old[o+common:], new[n+common:])
+	}
+
+	return result
+}
+
+// From: https://en.wikipedia.org/wiki/Longest_common_substring_problem
+func lcSubstr(S []string, T []string) (int, int, int) {
+	r := len(S)
+	n := len(T)
+	Lprev := make([]int, n)
+	Lnext := make([]int, n)
+	z := 0
+	retI := 0
+	retJ := 0
+
+	for i := 0; i < r; i++ {
+		for j := 0; j < n; j++ {
+			if S[i] == T[j] {
+				if j == 0 {
+					Lnext[j] = 1
+				} else {
+					Lnext[j] = Lprev[j-1] + 1
+				}
+				if Lnext[j] > z {
+					z = Lnext[j]
+					retI = i + 1
+					retJ = j + 1
+				}
+			} else {
+				Lnext[j] = 0
+			}
+		}
+		Lprev, Lnext = Lnext, Lprev
+	}
+
+	return retI - z, retJ - z, z
+}