diff --git a/R/conditions.R b/R/conditions.R
index 861b42c95..25f74d7f5 100644
--- a/R/conditions.R
+++ b/R/conditions.R
@@ -156,16 +156,31 @@ saveCallStackDigest <- function(callStack) {
 # in the list. The list is deduplicated by digest; ideally the digests on the
 # list are cached before calling this function (you will get a warning if not).
 appendCallStackWithDedupe <- function(lst, x) {
-  digests <- vapply(lst, getCallStackDigest, character(1), warn = TRUE)
-  xdigest <- getCallStackDigest(x, warn = FALSE)
-  stopifnot(all(nzchar(digests)))
-  stopifnot(length(xdigest) == 1)
-  stopifnot(nzchar(xdigest))
-  if (xdigest %in% digests) {
-    return(lst)
-  } else {
+  tryCatch({
+    digests <- vapply(lst, getCallStackDigest, character(1), warn = TRUE)
+    xdigest <- getCallStackDigest(x, warn = FALSE)
+    stopifnot(all(nzchar(digests)))
+    stopifnot(length(xdigest) == 1)
+    stopifnot(nzchar(xdigest))
+    if (xdigest %in% digests) {
+      return(lst)
+    } else {
+      return(c(lst, list(x)))
+    }
+  }, error = function(e) {
+    # Hopefully will never hit this. I'm only putting this in to be suuuper
+    # conservative about not letting our new deep stack trace dedupe logic crash
+    # the Shiny app.
+    if (in_devmode()) {
+      printError(e, full = TRUE)
+    }
+    rlang::warn(
+      "Failed to deduplicate deep stack traces; appending anyway",
+      .frequency = "once",
+      .frequency_id = "deepstack-deduplication-warning"
+    )
     return(c(lst, list(x)))
-  }
+  })
 }
 
 createStackTracePromiseDomain <- function() {