diff --git a/pkgs/development/python-modules/mypy/default.nix b/pkgs/development/python-modules/mypy/default.nix
index 85ceaf304c2..1b8d763eb6f 100644
--- a/pkgs/development/python-modules/mypy/default.nix
+++ b/pkgs/development/python-modules/mypy/default.nix
@@ -53,7 +53,8 @@ buildPythonPackage rec {
 
   # Compile mypy with mypyc, which makes mypy about 4 times faster. The compiled
   # version is also the default in the wheels on Pypi that include binaries.
-  MYPY_USE_MYPYC = "1";
+  # is64bit: unfortunately the build would exhaust all possible memory on i686-linux.
+  MYPY_USE_MYPYC = stdenv.buildPlatform.is64bit;
 
   meta = with stdenv.lib; {
     description = "Optional static typing for Python";