diff --git a/Makefile b/Makefile
index f4d9869..d94c7a9 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ TARGET	= picoc
 SRCS	= picoc.c table.c lex.c parse.c expression.c heap.c type.c \
 	variable.c clibrary.c platform.c include.c \
 	platform/platform_unix.c platform/library_unix.c \
-	cstdlib/stdio.c cstdlib/math.c
+	cstdlib/stdio.c cstdlib/math.c cstdlib/string.c
 OBJS	:= $(SRCS:%.c=%.o)
 
 all: depend $(TARGET)
diff --git a/cstdlib/stdio.c b/cstdlib/stdio.c
index 756883a..5026030 100644
--- a/cstdlib/stdio.c
+++ b/cstdlib/stdio.c
@@ -685,9 +685,14 @@ void StdioSetupFunc(void)
     VariableDefinePlatformVar(NULL, "stderr", FilePtrType, (union AnyValue *)&stderrValue, FALSE);
 
     /* define NULL, TRUE and FALSE */
-    VariableDefinePlatformVar(NULL, "NULL", &IntType, (union AnyValue *)&ZeroValue, FALSE);
-    VariableDefinePlatformVar(NULL, "TRUE", &IntType, (union AnyValue *)&TRUEValue, FALSE);
-    VariableDefinePlatformVar(NULL, "FALSE", &IntType, (union AnyValue *)&ZeroValue, FALSE);
+    if (!VariableDefined(TableStrRegister("NULL")))
+        VariableDefinePlatformVar(NULL, "NULL", &IntType, (union AnyValue *)&ZeroValue, FALSE);
+        
+    if (!VariableDefined(TableStrRegister("TRUE")))
+    {
+        VariableDefinePlatformVar(NULL, "TRUE", &IntType, (union AnyValue *)&TRUEValue, FALSE);
+        VariableDefinePlatformVar(NULL, "FALSE", &IntType, (union AnyValue *)&ZeroValue, FALSE);
+    }
 }
 
 /* portability-related I/O calls */
diff --git a/include.c b/include.c
index e42f157..6318de5 100644
--- a/include.c
+++ b/include.c
@@ -21,6 +21,10 @@ struct IncludeLibrary IncludeLibInfo[] =
         &MathSetupFunc, 
         &MathFunctions, 
         NULL },
+    { "string.h", 
+        &StringSetupFunc, 
+        &StringFunctions, 
+        NULL },
     { NULL, NULL, NULL, NULL }
 };
 
diff --git a/picoc.h b/picoc.h
index c07b228..94a99d7 100644
--- a/picoc.h
+++ b/picoc.h
@@ -421,4 +421,8 @@ void StdioSetupFunc(void);
 extern struct LibraryFunction MathFunctions[];
 void MathSetupFunc(void);
 
+/* string.c */
+extern struct LibraryFunction StringFunctions[];
+void StringSetupFunc(void);
+
 #endif /* PICOC_H */
diff --git a/tests/28_strings.c b/tests/28_strings.c
index 8ec7fc3..a4007af 100644
--- a/tests/28_strings.c
+++ b/tests/28_strings.c
@@ -1,15 +1,11 @@
 #include <stdio.h>
+#include <string.h>
 
 char a[10];
 
 strcpy(a, "hello");
 printf("%s\n", a);
 
-/*
-strcpy(&a, "there");
-printf("%s\n", a);
-*/
-
 strncpy(a, "gosh", 2);
 printf("%s\n", a);
 
@@ -29,7 +25,7 @@ printf("%d\n", strncmp(a, "zebra", 2));
 
 printf("%s\n", index(a, 'o'));
 printf("%s\n", rindex(a, 'l'));
-printf("%s\n", rindex(a, 'x'));
+printf("%d\n", rindex(a, 'x') == NULL);
 
 memset(&a[1], 'r', 4);
 printf("%s\n", a);
diff --git a/tests/28_strings.expect b/tests/28_strings.expect
index 5e19c73..422c6d6 100644
--- a/tests/28_strings.expect
+++ b/tests/28_strings.expect
@@ -11,7 +11,7 @@ gollo!
 -1
 ollo!
 lo!
-NULL
+1
 grrrr!
 grgrr!
 1
diff --git a/tests/29_array_address.c b/tests/29_array_address.c
index b81ce89..d70e116 100644
--- a/tests/29_array_address.c
+++ b/tests/29_array_address.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <string.h>
 
 char a[10];
 strcpy(a, "abcdef");