diff --git a/src/conf/janetconf.h b/src/conf/janetconf.h
index f31a8b35..eae3caa7 100644
--- a/src/conf/janetconf.h
+++ b/src/conf/janetconf.h
@@ -41,7 +41,8 @@
 /* #define JANET_API __attribute__((visibility ("default"))) */
 
 /* These settings should be specified before amalgamation is
- * built. */
+ * built. Any build with these set should be considered non-standard, and
+ * certain Janet libraries should be expected not to work. */
 /* #define JANET_NO_DOCSTRINGS */
 /* #define JANET_NO_SOURCEMAPS */
 /* #define JANET_REDUCED_OS */
@@ -51,13 +52,13 @@
 /* #define JANET_NO_NET */
 /* #define JANET_NO_TYPED_ARRAY */
 /* #define JANET_NO_INT_TYPES */
+/* #define JANET_NO_REALPATH */
+/* #define JANET_NO_SYMLINKS */
+/* #define JANET_NO_UMASK */
 
 /* Other settings */
 /* #define JANET_NO_PRF */
 /* #define JANET_NO_UTC_MKTIME */
-/* #define JANET_NO_REALPATH */
-/* #define JANET_NO_SYMLINKS */
-/* #define JANET_NO_UMASK */
 /* #define JANET_OUT_OF_MEMORY do { printf("janet out of memory\n"); exit(1); } while (0) */
 /* #define JANET_EXIT(msg) do { printf("C assert failed executing janet: %s\n", msg); exit(1); } while (0) */
 /* #define JANET_TOP_LEVEL_SIGNAL(msg) call_my_function((msg), stderr) */
diff --git a/src/core/os.c b/src/core/os.c
index 201d2930..1b794890 100644
--- a/src/core/os.c
+++ b/src/core/os.c
@@ -514,39 +514,11 @@ static Janet os_time(int32_t argc, Janet *argv) {
     return janet_wrap_number(dtime);
 }
 
-/* Clock shims */
-#ifdef JANET_WINDOWS
-static int gettime(struct timespec *spec) {
-    FILETIME ftime;
-    GetSystemTimeAsFileTime(&ftime);
-    int64_t wintime = (int64_t)(ftime.dwLowDateTime) | ((int64_t)(ftime.dwHighDateTime) << 32);
-    /* Windows epoch is January 1, 1601 apparently */
-    wintime -= 116444736000000000LL;
-    spec->tv_sec  = wintime / 10000000LL;
-    /* Resolution is 100 nanoseconds. */
-    spec->tv_nsec = wintime % 10000000LL * 100;
-    return 0;
-}
-#elif defined(__MACH__)
-static int gettime(struct timespec *spec) {
-    clock_serv_t cclock;
-    mach_timespec_t mts;
-    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
-    clock_get_time(cclock, &mts);
-    mach_port_deallocate(mach_task_self(), cclock);
-    spec->tv_sec = mts.tv_sec;
-    spec->tv_nsec = mts.tv_nsec;
-    return 0;
-}
-#else
-#define gettime(TV) clock_gettime(CLOCK_MONOTONIC, (TV))
-#endif
-
 static Janet os_clock(int32_t argc, Janet *argv) {
     janet_fixarity(argc, 0);
     (void) argv;
     struct timespec tv;
-    if (gettime(&tv)) janet_panic("could not get time");
+    if (janet_gettime(&tv)) janet_panic("could not get time");
     double dtime = tv.tv_sec + (tv.tv_nsec / 1E9);
     return janet_wrap_number(dtime);
 }
diff --git a/src/core/thread.c b/src/core/thread.c
index 54905135..d1d6cbab 100644
--- a/src/core/thread.c
+++ b/src/core/thread.c
@@ -234,7 +234,7 @@ static void janet_waiter_init(JanetWaiter *waiter, double sec) {
     if (waiter->timedwait) {
         /* N seconds -> timespec of (now + sec) */
         struct timespec now;
-        clock_gettime(CLOCK_REALTIME, &now);
+        janet_gettime(&now);
         time_t tvsec = (time_t) floor(sec);
         long tvnsec = (long) floor(1000000000.0 * (sec - ((double) tvsec)));
         tvsec += now.tv_sec;
diff --git a/src/core/util.c b/src/core/util.c
index cb8f5bb1..7277f95b 100644
--- a/src/core/util.c
+++ b/src/core/util.c
@@ -590,3 +590,35 @@ JanetTable *janet_get_core_table(const char *name) {
     if (!janet_checktype(out, JANET_TABLE)) return NULL;
     return janet_unwrap_table(out);
 }
+
+/* Clock shims for various platforms */
+#ifdef JANET_GETTIME
+#ifdef JANET_WINDOWS
+int janet_gettime(struct timespec *spec) {
+    FILETIME ftime;
+    GetSystemTimeAsFileTime(&ftime);
+    int64_t wintime = (int64_t)(ftime.dwLowDateTime) | ((int64_t)(ftime.dwHighDateTime) << 32);
+    /* Windows epoch is January 1, 1601 apparently */
+    wintime -= 116444736000000000LL;
+    spec->tv_sec  = wintime / 10000000LL;
+    /* Resolution is 100 nanoseconds. */
+    spec->tv_nsec = wintime % 10000000LL * 100;
+    return 0;
+}
+#elif defined(__MACH__)
+int janet_gettime(struct timespec *spec) {
+    clock_serv_t cclock;
+    mach_timespec_t mts;
+    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
+    clock_get_time(cclock, &mts);
+    mach_port_deallocate(mach_task_self(), cclock);
+    spec->tv_sec = mts.tv_sec;
+    spec->tv_nsec = mts.tv_nsec;
+    return 0;
+}
+#else
+int janet_gettime(struct timespec *spec) {
+    return clock_gettime(CLOCK_MONOTONIC, spec);
+}
+#endif
+#endif
diff --git a/src/core/util.h b/src/core/util.h
index c487622e..dd239a4b 100644
--- a/src/core/util.h
+++ b/src/core/util.h
@@ -97,6 +97,13 @@ void janet_core_def(JanetTable *env, const char *name, Janet x, const void *p);
 void janet_core_cfuns(JanetTable *env, const char *regprefix, const JanetReg *cfuns);
 #endif
 
+/* Clock gettime */
+#if !defined(JANET_REDUCED_OS) || !defined(JANET_SINGLE_THREADED)
+#include <time.h>
+#define JANET_GETTIME
+int janet_gettime(struct timespec *spec);
+#endif
+
 /* Initialize builtin libraries */
 void janet_lib_io(JanetTable *env);
 void janet_lib_math(JanetTable *env);