diff --git a/pkgs/development/compilers/gcc/4.9/default.nix b/pkgs/development/compilers/gcc/4.9/default.nix
index 14641faa5fe..9069387762f 100644
--- a/pkgs/development/compilers/gcc/4.9/default.nix
+++ b/pkgs/development/compilers/gcc/4.9/default.nix
@@ -320,7 +320,7 @@ stdenv.mkDerivation ({
       " --with-gnu-as --without-gnu-ld "
       else ""}
     --enable-lto
-    ${if enableMultilib then "--disable-libquadmath" else "--disable-multilib"}
+    ${if enableMultilib then "--enable-multilib --disable-libquadmath" else "--disable-multilib"}
     ${if enableShared then "" else "--disable-shared"}
     ${if enablePlugin then "--enable-plugin" else "--disable-plugin"}
     ${optionalString (isl != null) "--with-isl=${isl}"}
diff --git a/pkgs/development/compilers/gcc/5/default.nix b/pkgs/development/compilers/gcc/5/default.nix
index 5e6acea35df..46864c0bb02 100644
--- a/pkgs/development/compilers/gcc/5/default.nix
+++ b/pkgs/development/compilers/gcc/5/default.nix
@@ -318,7 +318,7 @@ stdenv.mkDerivation ({
       " --with-gnu-as --without-gnu-ld "
       else ""}
     --enable-lto
-    ${if enableMultilib then "--disable-libquadmath" else "--disable-multilib"}
+    ${if enableMultilib then "--enable-multilib --disable-libquadmath" else "--disable-multilib"}
     ${if enableShared then "" else "--disable-shared"}
     ${if enablePlugin then "--enable-plugin" else "--disable-plugin"}
     ${optionalString (isl != null) "--with-isl=${isl}"}