diff --git a/NEWS.md b/NEWS.md
index 0ac5e7c..6df2b89 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # hubEnsembles (development version)
 
+* Fix bug in `simple_ensemble()` where `all.equal()` was sometimes throwing an error (#134)
+
 # hubEnsembles 0.1.8
 
 * Update README to point to hubverse R-universe
diff --git a/R/simple_ensemble.R b/R/simple_ensemble.R
index 655d0c9..203b10a 100644
--- a/R/simple_ensemble.R
+++ b/R/simple_ensemble.R
@@ -94,7 +94,7 @@ simple_ensemble <- function(model_out_tbl, weights = NULL,
   }
 
   # don't interpolate when calling `matrixStats::weightedMedian`
-  if (isTRUE(all.equal(agg_fun, matrixStats::weightedMedian))) {
+  if (identical(agg_fun, matrixStats::weightedMedian)) {
     agg_args <- c(agg_args, list(interpolate = FALSE))
   }
 
diff --git a/tests/testthat/test-simple_ensemble.R b/tests/testthat/test-simple_ensemble.R
index 3d74274..740e417 100644
--- a/tests/testthat/test-simple_ensemble.R
+++ b/tests/testthat/test-simple_ensemble.R
@@ -281,3 +281,17 @@ test_that("duplicate forecast values still result in correct weighted median", {
 
   expect_equal(weighted_median_expected, weighted_median_actual)
 })
+
+test_that("simple_ensemble accepts custom functions without error", {
+  geometric_mean <- function(x) {
+    n <- length(x)
+    return(prod(x)^(1 / n))
+  }
+
+  model_outputs |>
+    hubEnsembles::simple_ensemble(
+      agg_fun = geometric_mean,
+      model_id = "simple-ensemble-geometric"
+    ) |>
+    expect_no_error()
+})