diff --git a/R/simple_slopes.R b/R/simple_slopes.R
index 76f9ee5..aad76e7 100644
--- a/R/simple_slopes.R
+++ b/R/simple_slopes.R
@@ -337,9 +337,7 @@ sim_slopes <- function(model, pred, modx, mod2 = NULL, modx.values = NULL,
   # Since output columns are conditional, I call summ here to see what they will
   # be. I set vifs = FALSE to make sure it isn't fit due to user options.
   # Need proper name for test statistic\
-  has_summ <- any(sapply(class(model), function(x) {
-      !is.null(getS3method("summ", x, optional = TRUE))
-    }))
+  has_summ <- check_method(summ, model)
   tcol <- try(colnames(summary(model)$coefficients)[3], silent = TRUE)
   if (!is.null(tcol) & class(tcol) != "try-error") {
     tcol <- gsub("value", "val.", tcol)
diff --git a/R/utils.R b/R/utils.R
index bf6c863..ed380af 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -284,3 +284,19 @@ j_update <- function(mod, formula = NULL, data = NULL, offset = NULL,
 
   eval(call, env, call.env)
 }
+
+# adapted from https://stackoverflow.com/a/42742370
+# Looking for whether a method is defined for a given object (...)
+# getS3method() doesn't work for something like merMod because the string
+# "merMod" is not in the vector returned by class()
+check_method <- function(generic, ...) {
+  ch <- deparse(substitute(generic))
+  f <- X <- function(x, ...) UseMethod("X")
+  for(m in methods(ch)) assign(sub(ch, "X", m, fixed = TRUE), "body<-"(f, value = m))
+  tryCatch({
+    X(...)
+    TRUE
+  }, error = function(e) {
+    FALSE
+  })
+}