diff --git a/R/session.R b/R/session.R
index 62c822c31..2a29550e8 100644
--- a/R/session.R
+++ b/R/session.R
@@ -63,9 +63,21 @@
 is_installed <- function(pkg, ..., version = NULL, compare = NULL) {
   check_dots_empty0(...)
 
+  # Fast path. Note that if `version` is supplied, this always falls through to the
+  # more expensive check.
+  if (is.null(version)) {
+    loaded <- lapply(pkg, function(x) {
+      is.character(x) && nzchar(x) && is.environment(.getNamespace(x))
+    })
+    if (all(as.logical(loaded))) {
+      return(TRUE)
+    }
+  }
+
   info <- pkg_version_info(pkg, version = version, compare = compare)
   all(detect_installed(info))
 }
+
 detect_installed <- function(info) {
   # Internal mechanism for unit tests
   hook <- peek_option("rlang:::is_installed_hook")