diff --git a/lisp/l/eusforeign.l b/lisp/l/eusforeign.l
index 910790cee..0664e4a88 100644
--- a/lisp/l/eusforeign.l
+++ b/lisp/l/eusforeign.l
@@ -148,6 +148,12 @@
 	(setf (symbol-function (intern (string-upcase fname)))
 	      (make-foreign-code fname nil :integer ,mod))))
 
+; mprotect(addr, len, prot) -- used to make trampoline pages executable on x86_64 Linux
+; wrapped in when because mprotect may not be in sysmod on non-Linux platforms (e.g. macOS)
+#+:x86_64
+(when (system::find-entry "mprotect" (sys::sysmod))
+  (defforeign c-mprotect (sys::sysmod) "mprotect" (:integer :integer :integer) :integer))
+
 ;(eval-when (compile)
 ;  (defclass foreign-pod :super symbol :slots (podcode paramtypes resulttype)))
 
@@ -370,6 +376,11 @@
 		    :start1 100)
            (if *debug* (format t "PODCODE ADDR: ~x~%" (+ 16 (sys:address podcode))))
 	   podcode)
+#+:x86_64
+   (when (fboundp 'c-mprotect)
+     (let* ((addr (sys:address podcode))
+            (page-addr (* (floor (/ addr 4096)) 4096)))
+       (c-mprotect page-addr (* 2 4096) 7)))
 #+:sh4 
 (progn
 	(setq podcode (byte-string
diff --git a/test/test-foreign.l b/test/test-foreign.l
index 9365c3365..9672d743e 100644
--- a/test/test-foreign.l
+++ b/test/test-foreign.l
@@ -549,22 +549,25 @@ test-testd = 1.23456
   (assert (= (ret-eusinteger 123 645000) (+ 123 645000)))
   )
 
-#|
-;; ret-int
-;; ret-short
-;; ret-char
-
-;; callback function
+;; callback function -- Linux x86_64 only
+;; trampoline machine code is x86_64-specific, and mprotect is needed to make
+;; the GC heap executable (not available in sysmod on macOS)
+#+(and :x86_64 :linux)
 (defun-c-callable LISP-IFUNC () :integer
   (format t "LISP-INTFUNC is called, return ~D~%" 1234)
   1234)
-;;
-(format t "~%callback function test(integer)~%")
-(format t "  callback function is set~%")
-(set-ifunc (pod-address 'LISP-IFUNC))
-(format t "  expected result: LISP-INTFUNC is called, return 1234~%")
-(format t "  call-ifunc = ~A~%" (call-ifunc))
 
+#+(and :x86_64 :linux)
+(deftest test-callback-integer ()
+  (format t "~%callback function test(integer)~%")
+  (format t "  callback function is set~%")
+  (set-ifunc (pod-address (intern "LISP-IFUNC")))
+  (format t "  expected result: LISP-INTFUNC is called, return 1234~%")
+  (let ((result (call-ifunc)))
+    (format t "  call-ifunc = ~A~%" result)
+    (assert (= result 1234))))
+
+#+(and :x86_64 :linux)
 (defun-c-callable LISP-FFUNC ((i0 :integer) (i1 :integer) (i2 :integer)
                               (i3 :integer) (i4 :integer) (i5 :integer)
                               (f0 :float) (f1 :float) (f2 :float) (f3 :float)
@@ -580,10 +583,13 @@ test-testd = 1.23456
   (format t "~A ~A~%" i6 i7)
   (format t "return ~A~%" 0.12345)
   0.12345)
-(format t "~%callback function test(float)~%")
-(format t "  callback function is set~%")
-(set-ffunc (pod-address 'LISP-FFUNC))
-(format t "  expected result: LISP-FFUNC is called
+
+#+(and :x86_64 :linux)
+(deftest test-callback-float ()
+  (format t "~%callback function test(float)~%")
+  (format t "  callback function is set~%")
+  (set-ffunc (pod-address (intern "LISP-FFUNC")))
+  (format t "  expected result: LISP-FFUNC is called
   100 101 102
   103 104 105
   1000.0 1010.0 1020.0 1030.0
@@ -591,8 +597,9 @@ test-testd = 1.23456
   2080.0 2090.0
   206 207
   return 0.12345~%")
-(format t "call-ffunc = ~A~%" (call-ffunc))
-|#
+  (let ((result (call-ffunc)))
+    (format t "call-ffunc = ~A~%" result)
+    (assert (< (abs (- result 0.12345)) 1e-4))))
 
 (eval-when (load eval)
   (run-all-tests)
diff --git a/test/test_foreign.c b/test/test_foreign.c
index 48f62bd2f..a41477d0a 100644
--- a/test/test_foreign.c
+++ b/test/test_foreign.c
@@ -337,6 +337,7 @@ long set_ifunc(long (*f) ())
 {
   g = f;
   printf("set_ifunc, g = %lX\n", g);
+  return 0;
 }
 
 long set_ffunc(double (*f) ())
@@ -348,6 +349,7 @@ long set_ffunc(double (*f) ())
                     double d8, double d9,
                     long i6, long i7))f;
   printf("set_ffunc, gf = %lX\n", gf);
+  return 0;
 }
 
 long call_ifunc() {