diff --git a/internal/impl/decode.go b/internal/impl/decode.go
index 85cc6b0..9ccfa7f 100644
--- a/internal/impl/decode.go
+++ b/internal/impl/decode.go
@@ -85,6 +85,9 @@
 		if n < 0 {
 			return 0, wire.ParseError(n)
 		}
+		if num > wire.MaxValidNumber {
+			return 0, errors.New("invalid field number")
+		}
 		b = b[n:]
 
 		var f *coderFieldInfo