diff --git a/lib83/ctype.c b/lib83/ctype.c
index db4fe4a..8b9b58d 100644
--- a/lib83/ctype.c
+++ b/lib83/ctype.c
@@ -12,7 +12,7 @@
 #define GRAPH 0x80
 
 // TODO.
-static unsigned char tab[256] = {
+static const unsigned char tab[256] = {
     GRAPH, LOWER|SPECL|ALPHA, LOWER|SPECL|ALPHA, LOWER|SPECL|ALPHA, LOWER|SPECL|ALPHA, GRAPH, GRAPH, GRAPH, SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, ALPHA|UPPER|SPECL,
     GRAPH|SPECL, SPECL, SPECL, GRAPH|SPECL, GRAPH|SPECL, GRAPH|SPECL, GRAPH|SPECL, SPECL, SPECL, SPECL, SPECL, SPECL, SPECL, SPECL, GRAPH|SPECL, GRAPH|SPECL,
     SPACE, PUNCT|SPECL, PUNCT|SPECL, SPECL|GRAPH, SPECL, SPECL|GRAPH, PUNCT|SPECL|GRAPH, PUNCT|SPECL|GRAPH, PUNCT|SPECL|GRAPH, PUNCT|SPECL|GRAPH, SPECL|GRAPH, SPECL|GRAPH, PUNCT|SPECL|GRAPH, SPECL|GRAPH, PUNCT|SPECL|GRAPH, SPECL|GRAPH,
diff --git a/lib83/stddef.h b/lib83/stddef.h
new file mode 100644
index 0000000..1429181
--- /dev/null
+++ b/lib83/stddef.h
@@ -0,0 +1,23 @@
+
+#ifndef _STDDEF_H
+#define _STDDEF_H
+
+#define NULL ((void *)0)
+
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned long uint32_t;
+
+typedef signed char int8_t;
+typedef signed short int16_t;
+typedef signed long int32_t;
+
+typedef uint16_t size_t;
+typedef int16_t ssize_t;
+typedef int16_t ptrdiff_t;
+
+#define true 1
+#define false 0
+
+#endif
+
diff --git a/lib83/string.h b/lib83/string.h
new file mode 100644
index 0000000..e69de29
diff --git a/main.c b/main.c
index f53dd5f..b3d8fd5 100644
--- a/main.c
+++ b/main.c
@@ -1,5 +1,7 @@
 #include <assert.h>
+#include <stddef.h>
 
 void main() {
-    assert(0);
+    bool b = 0;
+    assert(b);
 }