diff --git a/R/tinyformula.R b/R/tinyformula.R
index 56fd546e..29189061 100644
--- a/R/tinyformula.R
+++ b/R/tinyformula.R
@@ -74,6 +74,8 @@ tinyframe = function(formula, data, drop = FALSE) {
   ## - formula: (sub-)formula
   ## - data: model.frame from full formula
   if (is.null(formula)) return(NULL)
-  names = sapply(attr(terms(formula), "variables")[-1L], deparse, width.cutoff = 500L)
+  vars = attr(terms(formula), "variables")[-1L]
+  if (is.null(vars)) return(NULL)
+  names = sapply(vars, deparse, width.cutoff = 500L)
   data[, names, drop = drop]
 }
diff --git a/R/tinyplot.R b/R/tinyplot.R
index 1073a4c9..050b2a61 100644
--- a/R/tinyplot.R
+++ b/R/tinyplot.R
@@ -1429,13 +1429,14 @@ tinyplot.formula = function(
   m[[1L]] = quote(stats::model.frame)
   mf = eval.parent(m)
 
-  ## extract x
+  ## extract x (if any)
   x = tinyframe(tf$x, mf)
-  xnam = names(x)[[1L]]
-  if (length(names(x)) != 1L) warning(
-    paste("formula should specify exactly one x-variable, using:", xnam),
+  if (!is.null(x)) {
+    xnam = names(x)[[1L]]
+    if (length(names(x)) > 1L) warning(paste("formula should specify at most one x-variable, using:", xnam),
     "\nif you want to use arithmetic operators, make sure to wrap them inside I()")
-  x = x[[xnam]]
+    x = x[[xnam]]
+  }
 
   ## extract y (if any)
   y = tinyframe(tf$y, mf)