diff --git a/chibicc.h b/chibicc.h
index ac2348cdc809cd28e0582c09aec59f30b61fe9f3..23f122ed46212ef8ef42466a95224be60ec89f9f 100644
--- a/chibicc.h
+++ b/chibicc.h
@@ -15,6 +15,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <time.h>
 #include <unistd.h>
 
 #define MAX(x, y) ((x) < (y) ? (y) : (x))
diff --git a/preprocess.c b/preprocess.c
index ac2b2649b6205180d4e6191cbf3b3af62613ee8c..9b77b05ed7665634547eeac09ac93ab3c5b071a2 100644
--- a/preprocess.c
+++ b/preprocess.c
@@ -856,6 +856,21 @@ static Token *line_macro(Token *tmpl) {
   return new_num_token(tmpl->line_no, tmpl);
 }
 
+// __DATE__ is expanded to the current date, e.g. "May 17 2020".
+static char *format_date(struct tm *tm) {
+  static char mon[][4] = {
+    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
+  };
+
+  return format("\"%s %2d %d\"", mon[tm->tm_mon], tm->tm_mday, tm->tm_year + 1900);
+}
+
+// __TIME__ is expanded to the current time, e.g. "13:34:03".
+static char *format_time(struct tm *tm) {
+  return format("\"%02d:%02d:%02d\"", tm->tm_hour, tm->tm_min, tm->tm_sec);
+}
+
 void init_macros(void) {
   // Define predefined macros
   define_macro("_LP64", "1");
@@ -902,6 +917,11 @@ void init_macros(void) {
 
   add_builtin("__FILE__", file_macro);
   add_builtin("__LINE__", line_macro);
+
+  time_t now = time(NULL);
+  struct tm *tm = localtime(&now);
+  define_macro("__DATE__", format_date(tm));
+  define_macro("__TIME__", format_time(tm));
 }
 
 // Concatenate adjacent string literals into a single string literal
diff --git a/test/macro.c b/test/macro.c
index 9bb20d2083f504b0c655a5222f22a60f0827b7e9..261d1d754bcaae095b193cae513c40d612e176af 100644
--- a/test/macro.c
+++ b/test/macro.c
@@ -366,6 +366,9 @@ int main() {
   ASSERT(5, ({ int f0zz=5; CONCAT(f,0zz); }));
   ASSERT(5, ({ CONCAT(4,.57) + 0.5; }));
 
+  ASSERT(11, strlen(__DATE__));
+  ASSERT(8, strlen(__TIME__));
+
   printf("OK\n");
   return 0;
 }
diff --git a/test/test.h b/test/test.h
index af27f72445a9c29bfb055bd8cf3a2c1989b43a0d..f6fa2db3661ef432a122104e4230430488c0658d 100644
--- a/test/test.h
+++ b/test/test.h
@@ -9,3 +9,4 @@ int strncmp(char *p, char *q, long n);
 int memcmp(char *p, char *q, long n);
 void exit(int n);
 int vsprintf();
+long strlen(char *s);