diff --git a/index/li/libgmp/libgmp-external.toml b/index/li/libgmp/libgmp-external.toml
index b1aef287..1908af63 100644
--- a/index/li/libgmp/libgmp-external.toml
+++ b/index/li/libgmp/libgmp-external.toml
@@ -14,6 +14,7 @@ homebrew = ["gmp"]
 macports = ["gmp"]
 fedora = ["gmp-devel"]
 suse = ["gmp-devel"]
+gentoo = ["dev-libs/gmp"]
 
 [[external]]
 kind = "version-output"