diff --git a/flake.nix b/flake.nix
index 776ce98..04005ec 100644
--- a/flake.nix
+++ b/flake.nix
@@ -184,6 +184,16 @@
             (x: x?pname && x.pname != "perl-ldap")
             (old.propagatedBuildInputs or []);
         });
+        # clamav try_run fails cross-compile (cmake modules all use the same
+        # generic `test_run_result` cache variable name for FD passing, uname
+        # POSIX, struct packing, and signed right-shift checks).
+        # On aarch64 Linux (glibc + GCC) all four return 0, so pre-set it.
+        clamav = prev.clamav.overrideAttrs (old: {
+          cmakeFlags = (old.cmakeFlags or []) ++ [
+            "-Dtest_run_result=0"
+            "-Dtest_run_result__TRYRUN_OUTPUT="
+          ];
+        });
       };
 
       uconsoleRpiPipewireOverlay = final: prev: {