diff --git a/base83/error.go b/base83/error.go
index 3f1e663..54174f7 100644
--- a/base83/error.go
+++ b/base83/error.go
@@ -1,13 +1,10 @@
-// +build !go1.13
-
 package base83
 
 import "errors"
 
+// ErrInvalidInput is returned when the given input to decode is not valid base83.
 var ErrInvalidInput = errors.New("base83: invalid input")
-var ErrInvalidLength = errors.New("base83: invalid length")
 
-// invalidError returns ErrInvalidInput for the given rune and index
 func invalidError(r rune, i int) error {
 	// No stdlib support for wrapped errors, so return as-is pre-1.13
 	return ErrInvalidInput
diff --git a/base83/error_go1.13.go b/base83/error_go1.13.go
deleted file mode 100644
index 3f0a04c..0000000
--- a/base83/error_go1.13.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// +build go1.13
-
-package base83
-
-import "fmt"
-
-func invalidError(c rune, i int) error {
-	return fmt.Errorf("illegal rune %v at index %d: %w", c, i, ErrInvalidInput)
-}
diff --git a/decode.go b/decode.go
index 847704a..ad18f54 100644
--- a/decode.go
+++ b/decode.go
@@ -27,6 +27,7 @@ func Components(hash string) (x, y int, err error) {
 	return x, y, nil
 }
 
+// Decode returns an image of the given hash with the given size.
 func Decode(hash string, width, height int, punch int) (img image.Image, err error) {
 	numX, numY, err := Components(hash)
 	if err != nil {
diff --git a/error.go b/error.go
index b18c410..528858c 100644
--- a/error.go
+++ b/error.go
@@ -1,5 +1,3 @@
-// +build !go1.13
-
 package blurhash
 
 import "errors"
diff --git a/error_go1.13.go b/error_go1.13.go
deleted file mode 100644
index 0c408ea..0000000
--- a/error_go1.13.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// +build go1.13
-
-package blurhash
-
-import "fmt"
-
-func lengthError(expectedLength, actualLength int) error {
-	return fmt.Errorf("expected hash length %d but got %d: %w", expectedLength, actualLength, ErrInvalidHash)
-}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..500c810
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module github.com/bbrks/go-blurhash
+
+go 1.12
+
+require github.com/matryer/is v1.2.0
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..6378c9b
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/matryer/is v1.2.0 h1:92UTHpy8CDwaJ08GqLDzhhuixiBUUD1p3AU6PHddz4A=
+github.com/matryer/is v1.2.0/go.mod h1:2fLPjFQM9rhQ15aVEtbuwhJinnOqrmgXPNdZsdwlWXA=