diff --git a/Makefile b/Makefile
index 00ac8fc..6164d5b 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,9 @@
-CFLAGS  = -ggdb -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
-#CFLAGS  = -pg -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
-#CFLAGS  = -O3 -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
+ifneq ($(OS),Windows_NT)
+	DEFS = -D_POSIX_C_SOURCE=200112L
+endif
+CFLAGS  = $(DEFS) -ggdb -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
+#CFLAGS  = $(DEFS) -pg -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
+#CFLAGS  = $(DEFS) -O3 -std=c11 -Wall -Wextra -pedantic -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition
 LDFLAGS = -lm
 SOURCE  = main.c util.c tok.c lex.c ir.c parse.c runtime.c vm.c map.c
 HEADERS =        util.h tok.h lex.h ir.h parse.h runtime.h vm.h map.h
diff --git a/main.c b/main.c
index 8b196a2..7821136 100644
--- a/main.c
+++ b/main.c
@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "ir.h"
 #include "lex.h"
@@ -77,12 +78,21 @@ static Value fn_pow(Value *args) {
 		set_err("pow() requires arguments of type float");
 		return (Value){0};
 	}
-	return (Value) {
+	return (Value){
 		.type.kind = TypeFloat,
 		.Float = pow(args[0].Float, args[1].Float),
 	};
 }
 
+static Value fn_sleep(Value *args) {
+	if (!(args[0].type.kind == TypeFloat && args[0].Float >= 0.0)) {
+		set_err("sleep() requires a positive float");
+		return (Value){0};
+	}
+	sleep_secs(args[0].Float);
+	return (Value){0};
+}
+
 int main(int argc, const char **argv) {
 	/* parse arguments */
 	size_t nargs = argc - 1;
@@ -147,6 +157,7 @@ int main(int argc, const char **argv) {
 		{ .name = "int",   .side_effects = false, .n_args = 1, .func = fn_int,   },
 		{ .name = "float", .side_effects = false, .n_args = 1, .func = fn_float, },
 		{ .name = "pow",   .side_effects = false, .n_args = 2, .func = fn_pow,   },
+		{ .name = "sleep", .side_effects = true,  .n_args = 1, .func = fn_sleep, },
 	};
 	IRToks ir = parse(&tokens, funcs, sizeof(funcs) / sizeof(funcs[0]));
 	if (err) {
diff --git a/runtime.c b/runtime.c
index 2cf2d1f..8c6d8a3 100644
--- a/runtime.c
+++ b/runtime.c
@@ -41,7 +41,7 @@ Value eval_binary(IRInstr instr, const Value *lhs, const Value *rhs) {
 		}
 		case IREq:
 		case IRLt:
-		case IRLe:
+		case IRLe: {
 			bool res;
 			if (lhs->type.kind == TypeInt && rhs->type.kind == TypeInt) {
 				switch (instr) {
@@ -65,6 +65,7 @@ Value eval_binary(IRInstr instr, const Value *lhs, const Value *rhs) {
 				.type.kind = TypeBool,
 				.Bool = res,
 			};
+		}
 		case IRAnd:
 			return (Value){
 				.type.kind = TypeBool,
diff --git a/util.c b/util.c
index b16242b..cc7cd8e 100644
--- a/util.c
+++ b/util.c
@@ -2,6 +2,23 @@
 
 #include <stdarg.h>
 
+#ifdef WIN32
+#include <windows.h> /* Sleep */
+#else
+#include <time.h> /* nanosleep */
+#endif
+
+void sleep_secs(double secs) {
+#ifdef WIN32
+	Sleep(secs * 1000.0);
+#else
+	struct timespec ts;
+	ts.tv_sec = (time_t)secs;
+	ts.tv_nsec = (secs - (double)ts.tv_sec) * 1000000000.0;
+	nanosleep(&ts, NULL);
+#endif
+}
+
 char errbuf[ERRSZ];
 bool err;
 size_t err_ln, err_col;
diff --git a/util.h b/util.h
index 680d48f..195334b 100644
--- a/util.h
+++ b/util.h
@@ -6,7 +6,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
+
+#ifdef WIN32
+#include <windows.h> /* SSIZE_T */
+typedef SSIZE_T ssize_t;
+#else
+#include <unistd.h> /* ssize_t */
+#endif
 
 typedef uint8_t pseudo_void;
 
@@ -29,6 +35,8 @@ typedef uint8_t pseudo_void;
 
 #define C_RESET   "\x1b[m"
 
+void sleep_secs(double secs);
+
 #define ERRSZ 4096
 extern char errbuf[ERRSZ];
 extern bool err;