diff --git a/macros.rubygems b/macros.rubygems
index afd3f85..f6e830f 100644
--- a/macros.rubygems
+++ b/macros.rubygems
@@ -9,9 +9,10 @@
 # Prints gem_name-version string, by default joining %gem_name, %version and
 # %prerelease macros. When [custom_gem_name] is provided, the
 # custom_gem_name is joined with %custom_gem_name_version macro which needs
-# to be predegined.
+# to be predefined. Please note that for the version macros are the dashes
+# replaced by underscores.
 #
-%gem_name_version() %{?1}%{!?1:%{gem_name}}-%{?1:%{expand:%{%{1}_version}}}%{!?1:%{version}}%{?prerelease}
+%gem_name_version() %{?1}%{!?1:%{gem_name}}-%{?1:%{expand:%{%{gsub %{1} - _}_version}}}%{!?1:%{version}}%{?prerelease}
 
 # Common gem locations and files.
 #