diff --git a/R/ggplot.R b/R/ggplot.R
index 1512ad0b..a82a43a8 100644
--- a/R/ggplot.R
+++ b/R/ggplot.R
@@ -18,6 +18,7 @@ ggplot_build_set <- function() {
   ggplot_build <- getFromNamespace("ggplot_build", "ggplot2")
   .globals$ggplot_build <- getFromNamespace("ggplot_build.ggplot", "ggplot2")
   assign_in_namespace <- assignInNamespace
+  ensure_s3_methods_matrix()
   assign_in_namespace("ggplot_build.ggplot", ggthematic_build, "ggplot2")
 }
 
@@ -30,6 +31,15 @@ ggplot_build_restore <- function() {
   }
 }
 
+# Turns out that calling registerS3method() in an onLoad() hook causes
+# assignInNamespace() to no longer work, but here's a workaround for the issue
+# https://github.com/rstudio/thematic/issues/90#issuecomment-780224962
+ensure_s3_methods_matrix <- function(pkg = "ggplot2") {
+  S3 <- .getNamespaceInfo(asNamespace(pkg), "S3methods")
+  S3 <- matrix(as.character(S3), nrow = nrow(S3), ncol = ncol(S3))
+  setNamespaceInfo(asNamespace(pkg), "S3methods", S3)
+}
+
 # N.B. If you make changes here, plotly might have to as well!
 # https://github.com/ropensci/plotly/pull/1801/files#diff-3afd3a8e6a2cbc84a7afc6d2d06ec5e3R429
 ggthematic_build <- function(p, ggplot_build = NULL, theme = NULL) {