diff --git a/gnu/packages/commencement.scm b/gnu/packages/commencement.scm
index a7aeb04523..44ee252d1c 100644
--- a/gnu/packages/commencement.scm
+++ b/gnu/packages/commencement.scm
@@ -2120,6 +2120,9 @@ (define gcc-mesboot
     (native-inputs `(("gcc-wrapper" ,gcc-mesboot1-wrapper)
                      ("headers" ,glibc-headers-mesboot)
                      ,@(%boot-mesboot4-inputs)))
+    (inputs `(("gmp-source" ,(bootstrap-origin (package-source gmp-6.0)))
+              ("mpfr-source" ,(bootstrap-origin (package-source mpfr)))
+              ("mpc-source" ,(bootstrap-origin (package-source mpc)))))
     (arguments
      `(#:validate-runpath? #f
        ,@(substitute-keyword-arguments (package-arguments gcc-mesboot1)
@@ -2167,31 +2170,44 @@ (define gcc-mesboot
                 (delete 'apply-boot-patch)
                 (delete 'unpack-g++)     ; sadly, gcc-4.9.4 does not provide
                                                   ; modular core/language downloads
-                (replace 'setenv
+                (add-after 'unpack 'unpack-gmp&co
+                  (lambda* (#:key inputs #:allow-other-keys)
+                    (let ((gmp  (assoc-ref %build-inputs "gmp-source"))
+                          (mpfr (assoc-ref %build-inputs "mpfr-source"))
+                          (mpc  (assoc-ref %build-inputs "mpc-source")))
+
+                      ;; To reduce the set of pre-built bootstrap inputs, build
+                      ;; GMP & co. from GCC.
+                      (for-each (lambda (source)
+                                  (invoke "tar" "xvf" source))
+                                (list gmp mpfr mpc))
+
+                      ;; Create symlinks like `gmp' -> `gmp-x.y.z'.
+                      #$@(map (lambda (lib)
+                                ;; Drop trailing letters, as gmp-6.0.0a unpacks
+                                ;; into gmp-6.0.0.
+                                #~(symlink #$(string-trim-right
+                                              (package-full-name lib "-")
+                                              char-set:letter)
+                                           #$(package-name lib)))
+                              (list gmp-6.0 mpfr mpc)))))
+                (replace 'set-cplus-include-path
                   (lambda* (#:key outputs #:allow-other-keys)
-                    (let* ((out (assoc-ref outputs "out"))
-                           (binutils (assoc-ref %build-inputs "binutils"))
-                           (bash (assoc-ref %build-inputs "bash"))
-                           (gcc (assoc-ref %build-inputs "gcc"))
-                           (glibc (assoc-ref %build-inputs "libc"))
-                           (kernel-headers (assoc-ref %build-inputs "kernel-headers")))
+                    (let* ((bash (assoc-ref %build-inputs "bash"))
+                           (gcc (assoc-ref %build-inputs "gcc")))
                       (setenv "CONFIG_SHELL" (string-append bash "/bin/sh"))
                       (setenv "C_INCLUDE_PATH" (string-append
+                                                (getenv "C_INCLUDE_PATH") ":"
                                                 gcc "/lib/gcc-lib/"
                                                 #$(commencement-build-target)
                                                 "/4.6.4/include"
-                                                ":" kernel-headers "/include"
-                                                ":" glibc "/include"
                                                 ":" (getcwd) "/mpfr/src"))
                       (setenv "CPLUS_INCLUDE_PATH" (string-append
+                                                    (getenv "CPLUS_INCLUDE_PATH") ":"
                                                     gcc "/lib/gcc-lib/"
                                                     #$(commencement-build-target)
                                                     "/4.6.4/include"
-                                                    ":" kernel-headers "/include"
-                                                    ":" glibc "/include"
                                                     ":" (getcwd) "/mpfr/src"))
-                      (setenv "LIBRARY_PATH" (string-append glibc "/lib"
-                                                            ":" gcc "/lib"))
                       (format (current-error-port) "C_INCLUDE_PATH=~a\n" (getenv "C_INCLUDE_PATH"))
                       (format (current-error-port) "CPLUS_INCLUDE_PATH=~a\n" (getenv "CPLUS_INCLUDE_PATH"))
                       (format (current-error-port) "LIBRARY_PATH=~a\n"