diff --git a/R/do_call.R b/R/do_call.R
index 477d1fb..6cc5956 100644
--- a/R/do_call.R
+++ b/R/do_call.R
@@ -1,19 +1,25 @@
 # Updates the formals of a function with specified arguments before calling it.
 # Enables non-standard evaluation by allowing expressions in certain arguments.
-# Example: `do_call(func, list(args = bquote(.(constant_here) + symbol_here)))`
 do_call <- function(func, default = list(), fixed = list(), ...) {
-    # use `as.list()` because `formals()` returns a pairlist
-    formals <- as.environment(as.list(formals(func)))
+    # Use `as.list()` because `formals()` returns a pairlist.
+    args <- as.environment(as.list(formals(func)))
 
-    formal_names <- names(formals)
+    # Use `base::list2env()` over `utils::modifyList()` for minimal dependency.
+    args <- list2env(envir = args, default)
+    args <- list2env(envir = args, list(...))
+    args <- list2env(envir = args, fixed)
 
-    # use `base::list2env()` over `utils::modifyList()` for minimal dependency
-    formals <- list2env(envir = formals, default)
-    formals <- list2env(envir = formals, list(...))
-    formals <- list2env(envir = formals, fixed)
-
-    formals <- as.list.environment(formals, all.names = TRUE)[formal_names]
-
-    # `func` should be non-primitive
-    `formals<-`(func, value = formals)()
+    # `func` should be non-primitive.
+    `formals<-`(
+        func, value = lapply(
+            `names<-`(names(args), names(args)),
+            function(name) {
+                # `args[[name]]` might be a "missing symbol object". Always use the full form here.
+                # https://stackoverflow.com/questions/3892580
+                if (!is.language(args[[name]])) {
+                    bquote(parent.frame()$args[[.(name)]])
+                } else args[[name]]
+            }
+        )
+    )()
 }
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