diff --git a/accounts/abi/error.go b/accounts/abi/error.go
index 67739c21dc..afcd3dfed7 100644
--- a/accounts/abi/error.go
+++ b/accounts/abi/error.go
@@ -21,6 +21,10 @@ import (
 	"reflect"
 )
 
+var (
+	errBadBool error = "abi: improperly encoded boolean value"
+)
+
 // formatSliceString formats the reflection kind with the given slice size
 // and returns a formatted string representation.
 func formatSliceString(kind reflect.Kind, sliceSize int) string {
diff --git a/accounts/abi/unpack.go b/accounts/abi/unpack.go
index 2bb5c98606..fc41c88ac7 100644
--- a/accounts/abi/unpack.go
+++ b/accounts/abi/unpack.go
@@ -164,10 +164,10 @@ func readBool(word []byte) (bool, error) {
 	if len(word) != 32 {
 		return false, fmt.Errorf("abi: fatal error: incorrect word length")
 	}
-	improperEncoding := "abi: improperly encoded boolean value"
+
 	for i, b := range word {
 		if b != 0 && i != 31 {
-			return false, fmt.Errorf(improperEncoding)
+			return false, errBadBool
 		}
 	}
 	switch word[31] {
@@ -176,7 +176,7 @@ func readBool(word []byte) (bool, error) {
 	case 1:
 		return true, nil
 	default:
-		return false, fmt.Errorf(improperEncoding)
+		return false, errBadBool
 	}
 
 }