diff --git a/argparse.c b/argparse.c
index ec86bba7..02df0393 100644
--- a/argparse.c
+++ b/argparse.c
@@ -47,10 +47,11 @@ argparse_error(struct argparse *self, const struct argparse_option *opt,
 }
 
 static int
-argparse_getvalue(struct argparse *self, const struct argparse_option *opt,
+argparse_getvalue(struct argparse *self, struct argparse_option *opt,
                   int flags)
 {
     const char *s = NULL;
+    opt->parsed = 1;
     if (!opt->value)
         goto skipped;
     switch (opt->type) {
@@ -147,7 +148,7 @@ argparse_options_check(const struct argparse_option *options)
 }
 
 static int
-argparse_short_opt(struct argparse *self, const struct argparse_option *options)
+argparse_short_opt(struct argparse *self, struct argparse_option *options)
 {
     for (; options->type != ARGPARSE_OPT_END; options++) {
         if (options->short_name == *self->optvalue) {
@@ -159,7 +160,7 @@ argparse_short_opt(struct argparse *self, const struct argparse_option *options)
 }
 
 static int
-argparse_long_opt(struct argparse *self, const struct argparse_option *options)
+argparse_long_opt(struct argparse *self, struct argparse_option *options)
 {
     for (; options->type != ARGPARSE_OPT_END; options++) {
         const char *rest;
@@ -218,9 +219,22 @@ argparse_describe(struct argparse *self, const char *description,
     self->epilog      = epilog;
 }
 
+void argparse_check_for_required(struct argparse *self, struct argparse_option *options) {
+    for(; options->type != ARGPARSE_OPT_END; options++) {
+        // printf("checking %s %d %d\n", options->long_name, options->parsed, options->flags);
+        if((options->flags & OPT_REQUIRED) == OPT_REQUIRED && !options->parsed) {
+            // error => required option not parsed
+            fprintf(stderr, "error: option `%s` required\n", options->long_name);
+            argparse_usage(self);
+            exit(1);
+        }
+    }
+}
+
 int
 argparse_parse(struct argparse *self, int argc, const char **argv)
 {
+
     self->argc = argc - 1;
     self->argv = argv + 1;
     self->out  = argv;
@@ -278,6 +292,9 @@ argparse_parse(struct argparse *self, int argc, const char **argv)
     }
 
 end:
+    // check required options and exit if not all flags are satisfied
+    argparse_check_for_required(self, self->options);
+
     memmove(self->out + self->cpidx, self->argv,
             self->argc * sizeof(*self->out));
     self->out[self->cpidx + self->argc] = NULL;
@@ -302,7 +319,7 @@ argparse_usage(struct argparse *self)
 
     fputc('\n', stdout);
 
-    const struct argparse_option *options;
+    struct argparse_option *options;
 
     // figure out best width
     size_t usage_opts_width = 0;
diff --git a/argparse.h b/argparse.h
index 44ce835a..0a9c9e77 100644
--- a/argparse.h
+++ b/argparse.h
@@ -40,6 +40,7 @@ enum argparse_option_type {
 
 enum argparse_option_flags {
     OPT_NONEG = 1,              /* disable negation */
+    OPT_REQUIRED
 };
 
 /**
@@ -70,6 +71,9 @@ enum argparse_option_flags {
  *
  *  `flags`:
  *    option flags.
+ * 
+ *  *  `parsed`:
+ *    boolean to see if the option showed up in the argument list.
  */
 struct argparse_option {
     enum argparse_option_type type;
@@ -80,6 +84,7 @@ struct argparse_option {
     argparse_callback *callback;
     intptr_t data;
     int flags;
+    int parsed;
 };
 
 /**
@@ -87,7 +92,7 @@ struct argparse_option {
  */
 struct argparse {
     // user supplied
-    const struct argparse_option *options;
+    struct argparse_option *options;
     const char *const *usages;
     int flags;
     const char *description;    // a description after usage
@@ -105,13 +110,14 @@ int argparse_help_cb(struct argparse *self,
                      const struct argparse_option *option);
 
 // built-in option macros
-#define OPT_END()        { ARGPARSE_OPT_END, 0, NULL, NULL, 0, NULL, 0, 0 }
-#define OPT_BOOLEAN(...) { ARGPARSE_OPT_BOOLEAN, __VA_ARGS__ }
-#define OPT_BIT(...)     { ARGPARSE_OPT_BIT, __VA_ARGS__ }
-#define OPT_INTEGER(...) { ARGPARSE_OPT_INTEGER, __VA_ARGS__ }
-#define OPT_FLOAT(...)   { ARGPARSE_OPT_FLOAT, __VA_ARGS__ }
-#define OPT_STRING(...)  { ARGPARSE_OPT_STRING, __VA_ARGS__ }
-#define OPT_GROUP(h)     { ARGPARSE_OPT_GROUP, 0, NULL, NULL, h, NULL, 0, 0 }
+// initially all parsed values for options are 0
+#define OPT_END()        { ARGPARSE_OPT_END, 0, NULL, NULL, 0, NULL, 0, 0, 0 }
+#define OPT_BOOLEAN(...) { ARGPARSE_OPT_BOOLEAN, __VA_ARGS__, 0 }
+#define OPT_BIT(...)     { ARGPARSE_OPT_BIT, __VA_ARGS__, 0 }
+#define OPT_INTEGER(...) { ARGPARSE_OPT_INTEGER, __VA_ARGS__, 0 }
+#define OPT_FLOAT(...)   { ARGPARSE_OPT_FLOAT, __VA_ARGS__, 0 }
+#define OPT_STRING(...)  { ARGPARSE_OPT_STRING, __VA_ARGS__, 0 }
+#define OPT_GROUP(h)     { ARGPARSE_OPT_GROUP, 0, NULL, NULL, h, NULL, 0, 0, 0 }
 #define OPT_HELP()       OPT_BOOLEAN('h', "help", NULL,                 \
                                      "show this help message and exit", \
                                      argparse_help_cb, 0, OPT_NONEG)