diff --git a/src/calibre/ebooks/conversion/utils.py b/src/calibre/ebooks/conversion/utils.py
index f6e259b6f9..d4b03b8d55 100644
--- a/src/calibre/ebooks/conversion/utils.py
+++ b/src/calibre/ebooks/conversion/utils.py
@@ -375,9 +375,9 @@ class HeuristicProcessor(object):
         html = re.sub('<p\s?/>', '', html)
         # Get rid of empty span, bold, font, em, & italics tags
         html = re.sub(r"\s*<span[^>]*>\s*(<span[^>]*>\s*</span>){0,2}\s*</span>\s*", " ", html)
-        html = re.sub(r"\s*<(font|[ibu]|em)[^>]*>\s*(<(font|[ibu]|em)[^>]*>\s*</(font|[ibu]|em)>\s*){0,2}\s*</(font|[ibu]|em)>", " ", html)
+        html = re.sub(r"\s*<(font|[ibu]|em|strong)[^>]*>\s*(<(font|[ibu]|em|strong)[^>]*>\s*</(font|[ibu]|em|strong)>\s*){0,2}\s*</(font|[ibu]|em|strong)>", " ", html)
         html = re.sub(r"\s*<span[^>]*>\s*(<span[^>]>\s*</span>){0,2}\s*</span>\s*", " ", html)
-        html = re.sub(r"\s*<(font|[ibu]|em)[^>]*>\s*(<(font|[ibu]|em)[^>]*>\s*</(font|[ibu]|em)>\s*){0,2}\s*</(font|[ibu]|em)>", " ", html)
+        html = re.sub(r"\s*<(font|[ibu]|em|strong)[^>]*>\s*(<(font|[ibu]|em|strong)[^>]*>\s*</(font|[ibu]|em|strong)>\s*){0,2}\s*</(font|[ibu]|em|strong)>", " ", html)
         self.deleted_nbsps = True
         return html