diff --git a/R/glue.R b/R/glue.R
index 0a7693c..2b97ffc 100644
--- a/R/glue.R
+++ b/R/glue.R
@@ -97,6 +97,7 @@ glue_data <- function(.x, ..., .sep = "", .envir = parent.frame(),
 
   # Perform all evaluations in a temporary environment
   if (is.null(.x)) {
+    stopifnot(is.environment(.envir))
     parent_env <- .envir
   } else if (is.environment(.x)) {
     parent_env <- .x