diff --git a/stand/powerpc/ofw/cas.c b/stand/powerpc/ofw/cas.c
index 0a12f31d1a1a..e95af42762a5 100644
--- a/stand/powerpc/ofw/cas.c
+++ b/stand/powerpc/ofw/cas.c
@@ -234,9 +234,15 @@ ppc64_cas(void)
 		}
 	}
 
-	if ((var = getenv("radix_mmu")) != NULL && var[0] == '0')
+	if (!radix_mmu)
+		/*
+		 * If radix is not supported, set radix_mmu to 0 to avoid
+		 * the kernel trying to use it and panic.
+		 */
+		setenv("radix_mmu", "0", 1);
+	else if ((var = getenv("radix_mmu")) != NULL && var[0] == '0')
 		radix_mmu = 0;
-	if (radix_mmu)
+	else
 		ov5[OV5_MMU_INDEX] = OV5_MMU_RADIX;
 
 	inst = OF_open("/");