diff --git a/bigintHelpers.go.tmpl b/bigintHelpers.go.tmpl
index d0675ea..6413aff 100644
--- a/bigintHelpers.go.tmpl
+++ b/bigintHelpers.go.tmpl
@@ -24,13 +24,29 @@ func (b BigInt) MarshalText() ([]byte, error) {
 
 // UnmarshalText implements encoding.TextUnmarshaler.
 func (b *BigInt) UnmarshalText(text []byte) error {
-	t := string(text)
-	if len(text) <= 2 || t == "null" || t == "" {
+	if len(text) == 0 {
 		return nil
 	}
-	i, ok := big.NewInt(0).SetString(string(text[1:len(text)-1]), 10)
+	if len(text) == 4 && text[0] == 'n' && string(text) == "null" {
+		return nil
+	}
+	for _, c := range text {
+		if c == ' ' || c == '\t' || c == '\n' || c == '\r' {
+			return fmt.Errorf("BigInt.UnmarshalText: unexpected whitespace in %q", text)
+		}
+	}
+	var digits []byte
+	if text[0] == '-' || (text[0] >= '0' && text[0] <= '9') {
+		digits = text
+	} else {
+		if len(text) < 2 || text[0] != '"' || text[len(text)-1] != '"' {
+			return fmt.Errorf("BigInt.UnmarshalText: unsupported format %q", text)
+		}
+		digits = text[1 : len(text)-1]
+	}
+	i, ok := big.NewInt(0).SetString(string(digits), 10)
 	if !ok {
-		return fmt.Errorf("BigInt.UnmarshalText: failed to unmarshal %q", text)
+		return fmt.Errorf("BigInt.UnmarshalText: failed to parse %q", text)
 	}
 	*b = BigInt(*i)
 	return nil