diff --git a/var/spack/repos/builtin/packages/opencascade/package.py b/var/spack/repos/builtin/packages/opencascade/package.py
index 5801b8e1d85..c275a9f4306 100644
--- a/var/spack/repos/builtin/packages/opencascade/package.py
+++ b/var/spack/repos/builtin/packages/opencascade/package.py
@@ -182,7 +182,7 @@ def use_3rdparty(feature, spack_variant=None, depends_on=None, extra_dirs=[]):
         args.append("-DBUILD_DOC_Overview=OFF")
 
         # Always build the foundation classes
-        args.append(self.define("BUILD_MODULE_FoundationClasses", true))
+        args.append(self.define("BUILD_MODULE_FoundationClasses", True))
         # Specify which modules to build
         for module in [
             "ApplicationFramework",