diff --git a/overlay.nix b/overlay.nix
index 7a4eb27..bab8497 100644
--- a/overlay.nix
+++ b/overlay.nix
@@ -25,6 +25,7 @@ final: prev:
     # Override preboot to set 'bootcmd' directly to the kernel address in RAM
     extraConfig = ''
       CONFIG_PREBOOT="setenv fdt_addr ''${fdtcontroladdr}; fdt addr ''${fdtcontroladdr}; setenv bootcmd booti ''${kernel_addr_r} - ''${fdtcontroladdr};"
+      CONFIG_RISCV_ISA_C=n
     '';
   };
 
@@ -67,6 +68,8 @@ final: prev:
       PCI = yes;
       VIRTIO_PCI = yes;
       PCI_HOST_GENERIC = yes;
+
+      RISCV_ISA_C = no;
     };
   });
 }