diff --git a/include/intset.h b/include/intset.h
new file mode 100644
index 0000000..9ffa234
--- /dev/null
+++ b/include/intset.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2020 Andri Yngvason
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#pragma once
+
+#include <unistd.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+struct intset {
+	size_t cap;
+	size_t len;
+	int32_t* storage;
+};
+
+int intset_init(struct intset* self, size_t cap);
+void intset_destroy(struct intset* self);
+
+int intset_set(struct intset* self, int32_t value);
+void intset_clear(struct intset* self, int32_t value);
+
+bool intset_is_set(const struct intset* self, int32_t value);
diff --git a/meson.build b/meson.build
index 73480ef..9f10d31 100644
--- a/meson.build
+++ b/meson.build
@@ -59,6 +59,7 @@ sources = [
 	'src/seat.c',
 	'src/smooth.c',
 	'src/cfg.c',
+	'src/intset.c',
 ]
 
 dependencies = [
diff --git a/src/intset.c b/src/intset.c
new file mode 100644
index 0000000..1bec9ab
--- /dev/null
+++ b/src/intset.c
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2020 Andri Yngvason
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "intset.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#define DEFAULT_CAPACITY 256
+
+int intset_init(struct intset* self, size_t cap)
+{
+	if (cap == 0)
+		cap = DEFAULT_CAPACITY;
+
+	memset(self, 0, sizeof(*self));
+
+	self->storage = malloc(cap * sizeof(*self->storage));
+	if (!self->storage)
+		return -1;
+
+	self->cap = cap;
+
+	return 0;
+}
+
+void intset_destroy(struct intset* self)
+{
+	free(self->storage);
+	memset(self, 0, sizeof(*self));
+}
+
+static int intset__grow(struct intset*  self)
+{
+	size_t new_cap = self->cap * 2;
+
+	int32_t* new_storage = realloc(self->storage, new_cap);
+	if (!new_storage)
+		return -1;
+
+	self->storage = new_storage;
+	self->cap = new_cap;
+
+	return 0;
+}
+
+int intset_set(struct intset* self, int32_t value)
+{
+	if (intset_is_set(self, value))
+		return 0;
+
+	if (self->len >= self->cap && intset__grow(self) < 0)
+		return -1;
+
+	self->storage[self->len++] = value;
+
+	return 0;
+}
+
+static ssize_t intset__find_index(const struct intset* self, int32_t value)
+{
+	for (size_t i = 0; i < self->len; ++i)
+		if (self->storage[i] == value)
+			return i;
+
+	return -1;
+}
+
+void intset_clear(struct intset* self, int32_t value)
+{
+	ssize_t index = intset__find_index(self, value);
+	if (index < 0)
+		return;
+
+	self->storage[index] = self->storage[--self->len];
+}
+
+bool intset_is_set(const struct intset* self, int32_t value)
+{
+	return intset__find_index(self, value) >= 0;
+}