diff --git a/src/c/Makefile.in b/src/c/Makefile.in
index 46a5873ae..223f8fcae 100644
--- a/src/c/Makefile.in
+++ b/src/c/Makefile.in
@@ -50,7 +50,7 @@ HFILES = $(HDIR)/config.h $(HDIR)/ecl.h $(HDIR)/ecl-cmp.h $(HDIR)/object.h
 	$(HDIR)/impl/math_dispatch.h $(HDIR)/impl/math_fenv.h                   \
 	$(HDIR)/impl/math_fenv_msvc.h
 
-NUCL_OBJS = nucleus/error.o
+NUCL_OBJS = nucleus/error.o nucleus/runtime.o
 
 CLOS_OBJS = clos/cache.o clos/accessor.o clos/instance.o clos/gfun.o
 
diff --git a/src/c/main.d b/src/c/main.d
index 2774d4485..1cdd89060 100644
--- a/src/c/main.d
+++ b/src/c/main.d
@@ -55,80 +55,8 @@ const char *ecl_self;
 
 /************************ GLOBAL INITIALIZATION ***********************/
 
-
-/* HEAP */
-
-#if ECL_FIXNUM_BITS <= 32
-/* 1GB */
-#define HEAP_SIZE_DEFAULT 1073741824L
-#else
-/* 4GB */
-#define HEAP_SIZE_DEFAULT 4294967296L
-#endif
-
-
 static int ARGC;
 static char **ARGV;
-/* INV: see ecl_option enum in external.h */
-cl_fixnum ecl_option_values[ECL_OPT_LIMIT+1] = {
-#ifdef GBC_BOEHM_GENGC
-  1,              /* ECL_OPT_INCREMENTAL_GC */
-#else
-  0,              /* ECL_OPT_INCREMENTAL_GC */
-#endif
-  1,              /* ECL_OPT_TRAP_SIGSEGV */
-  1,              /* ECL_OPT_TRAP_SIGFPE */
-  1,              /* ECL_OPT_TRAP_SIGINT */
-  1,              /* ECL_OPT_TRAP_SIGILL */
-  1,              /* ECL_OPT_TRAP_SIGBUS */
-  1,              /* ECL_OPT_TRAP_SIGPIPE */
-  1,              /* ECL_OPT_TRAP_INTERRUPT_SIGNAL */
-  1,              /* ECL_OPT_SIGNAL_HANDLING_THREAD */
-  16,             /* ECL_OPT_SIGNAL_QUEUE_SIZE */
-  0,              /* ECL_OPT_BOOTED */
-  8192,           /* ECL_OPT_BIND_STACK_SIZE */
-  1024,           /* ECL_OPT_BIND_STACK_SAFETY_AREA */
-  2048,           /* ECL_OPT_FRAME_STACK_SIZE */
-  128,            /* ECL_OPT_FRAME_STACK_SAFETY_AREA */
-  32768,          /* ECL_OPT_LISP_STACK_SIZE */
-  128,            /* ECL_OPT_LISP_STACK_SAFETY_AREA */
-  ECL_DEFAULT_C_STACK_SIZE, /* ECL_OPT_C_STACK_SIZE */
-  4*sizeof(cl_index)*1024, /* ECL_OPT_C_STACK_SAFETY_AREA */
-  HEAP_SIZE_DEFAULT, /* ECL_OPT_HEAP_SIZE */
-  1024*1024,      /* ECL_OPT_HEAP_SAFETY_AREA */
-  0,              /* ECL_OPT_THREAD_INTERRUPT_SIGNAL */
-  1,              /* ECL_OPT_SET_GMP_MEMORY_FUNCTIONS */
-  1,              /* ECL_OPT_USE_SETMODE_ON_FILES */
-  0};
-
-#if !defined(GBC_BOEHM)
-static char stdin_buf[BUFSIZ];
-static char stdout_buf[BUFSIZ];
-#endif
-
-cl_fixnum
-ecl_get_option(int option)
-{
-  if (option >= ECL_OPT_LIMIT || option < 0) {
-    FEerror("Invalid boot option ~D", 1, ecl_make_fixnum(option));
-  }
-  return ecl_option_values[option];
-}
-
-void
-ecl_set_option(int option, cl_fixnum value)
-{
-  if (option > ECL_OPT_LIMIT || option < 0) {
-    FEerror("Invalid boot option ~D", 1, ecl_make_fixnum(option));
-  } else {
-    if (option < ECL_OPT_BOOTED &&
-        ecl_option_values[ECL_OPT_BOOTED]) {
-      FEerror("Cannot change option ~D while ECL is running",
-              1, ecl_make_fixnum(option));
-    } 
-    ecl_option_values[option] = value;
-  }
-}
 
 static void
 init_env_mp(cl_env_ptr env)
diff --git a/src/c/nucleus/runtime.c b/src/c/nucleus/runtime.c
new file mode 100644
index 000000000..4390916ba
--- /dev/null
+++ b/src/c/nucleus/runtime.c
@@ -0,0 +1,77 @@
+
+/* -- imports ------------------------------------------------------- */
+
+#include <ecl/ecl.h>
+#include <ecl/internal.h>
+
+/* -- implementation------------------------------------------------- */
+
+#if ECL_FIXNUM_BITS <= 32
+/* 1GB */
+#define ECL_DEFAULT_HEAP_SIZE 1073741824L
+#else
+/* 4GB */
+#define ECL_DEFAULT_HEAP_SIZE 4294967296L
+#endif
+
+#ifndef ECL_DEFAULT_C_STACK_SIZE
+#define ECL_DEFAULT_C_STACK_SIZE 0
+#endif
+
+#ifdef GBC_BOEHM_GENGC
+#define ECL_INCREMENTAL_GC 1
+#else
+#define ECL_INCREMENTAL_GC 0
+#endif
+
+/* INV: see ecl_option enum in external.h */
+cl_fixnum ecl_option_values[ECL_OPT_LIMIT+1] = {
+  /* ---------------------------------------------------------------- */
+  ECL_INCREMENTAL_GC,           /* ECL_OPT_INCREMENTAL_GC             */
+  1,                            /* ECL_OPT_TRAP_SIGSEGV               */
+  1,                            /* ECL_OPT_TRAP_SIGFPE                */
+  1,                            /* ECL_OPT_TRAP_SIGINT                */
+  1,                            /* ECL_OPT_TRAP_SIGILL                */
+  1,                            /* ECL_OPT_TRAP_SIGBUS                */
+  1,                            /* ECL_OPT_TRAP_SIGPIPE               */
+  1,                            /* ECL_OPT_TRAP_INTERRUPT_SIGNAL      */
+  1,                            /* ECL_OPT_SIGNAL_HANDLING_THREAD     */
+  16,                           /* ECL_OPT_SIGNAL_QUEUE_SIZE          */
+  0,                            /* ECL_OPT_BOOTED                     */
+  /* ---------------------------------------------------------------- */
+  8192,                         /* ECL_OPT_BIND_STACK_SIZE            */
+  1024,                         /* ECL_OPT_BIND_STACK_SAFETY_AREA     */
+  2048,                         /* ECL_OPT_FRAME_STACK_SIZE           */
+  128,                          /* ECL_OPT_FRAME_STACK_SAFETY_AREA    */
+  32768,                        /* ECL_OPT_LISP_STACK_SIZE            */
+  128,                          /* ECL_OPT_LISP_STACK_SAFETY_AREA     */
+  ECL_DEFAULT_C_STACK_SIZE,     /* ECL_OPT_C_STACK_SIZE               */
+  4*sizeof(cl_index)*1024,      /* ECL_OPT_C_STACK_SAFETY_AREA        */
+  ECL_DEFAULT_HEAP_SIZE,        /* ECL_OPT_HEAP_SIZE                  */
+  1024*1024,                    /* ECL_OPT_HEAP_SAFETY_AREA           */
+  0,                            /* ECL_OPT_THREAD_INTERRUPT_SIGNAL    */
+  1,                            /* ECL_OPT_SET_GMP_MEMORY_FUNCTIONS   */
+  1,                            /* ECL_OPT_USE_SETMODE_ON_FILES       */
+  /* ---------------------------------------------------------------- */
+  0};
+
+cl_fixnum
+ecl_get_option(int option)
+{
+  if (option >= ECL_OPT_LIMIT || option < 0) {
+    return -1;
+  }
+  return ecl_option_values[option];
+}
+
+cl_fixnum
+ecl_set_option(int option, cl_fixnum value)
+{
+  if (option > ECL_OPT_LIMIT || option < 0) {
+    return -1;
+  }
+  if (option >= ECL_OPT_BOOTED || !ecl_option_values[ECL_OPT_BOOTED]) {
+    ecl_option_values[option] = value;
+  }
+  return ecl_option_values[option];
+}
diff --git a/src/h/external.h b/src/h/external.h
index f59a55a4e..dde5dfa2a 100755
--- a/src/h/external.h
+++ b/src/h/external.h
@@ -977,7 +977,7 @@ typedef enum {
 } ecl_option;
 
 extern ECL_API const char *ecl_self;
-extern ECL_API void ecl_set_option(int option, cl_fixnum value);
+extern ECL_API cl_fixnum ecl_set_option(int option, cl_fixnum value);
 extern ECL_API cl_fixnum ecl_get_option(int option);
 extern ECL_API int cl_boot(int argc, char **argv);
 extern ECL_API void cl_shutdown(void);