diff --git a/bootfiles/18c/boot7.lisp b/bootfiles/18c/boot7.lisp
new file mode 100644
index 0000000000000000000000000000000000000000..92124a06e21ba33af336df77f38d73e75129ed87
--- /dev/null
+++ b/bootfiles/18c/boot7.lisp
@@ -0,0 +1,10 @@
+;; Add the constants for precision control on x86.
+;;
+#+x86
+(in-package :x86)
+#+x86
+(progn
+  (defconstant float-precision-24-bit  0)
+  (defconstant float-precision-53-bit  2)
+  (defconstant float-precision-64-bit  3))
+