diff --git a/internal/helpers/encode.go b/internal/helpers/encode.go
index 0df305e..ce141eb 100644
--- a/internal/helpers/encode.go
+++ b/internal/helpers/encode.go
@@ -13,7 +13,9 @@ import (
 )
 
 func EncodeValue(v attr.Value) (any, error) {
-	if v.IsNull() {
+	// Avoid nil pointer deref with broken OpenTofu custom function
+	// implementation that passes unknown values as zero values.
+	if v == nil || v.IsNull() {
 		return nil, nil
 	}