diff --git a/CMakeLists.txt b/CMakeLists.txt
index fb36ff9..c44851b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,9 +4,12 @@ project(forth C)
 set(CMAKE_C_STANDARD 99)
 
 add_executable(forth
-    main.c
-    fh_builtins.c
-    fh_runtime.c
-    fh_stack.c
-    fh_mem.c
+    src/main.c
+    src/fh_builtins.c
+    src/fh_runtime.c
+    src/fh_stack.c
+    src/fh_mem.c
 )
+
+target_include_directories(forth PRIVATE include)
+
diff --git a/build.sh b/build.sh
index e4411be..61c1023 100755
--- a/build.sh
+++ b/build.sh
@@ -1,3 +1,3 @@
 #!/bin/bash
 
-cc *.c -o forth
+cc -I include src/*.c -o forth
diff --git a/forth b/forth
index 86a2b5d..b4f3a2d 100755
Binary files a/forth and b/forth differ
diff --git a/forth.h b/forth.h
deleted file mode 100644
index 00e0d8f..0000000
--- a/forth.h
+++ /dev/null
@@ -1,48 +0,0 @@
-/**
- * TODO file description
- *
- * Created on 2021/11/13.
- */
-
-#ifndef FORTH_H
-#define FORTH_H
-
-#include <stdint.h>
-#include <stdbool.h>
-
-/* for printing */
-#include <stdlib.h>
-#include <stdio.h>
-
-#include "fh_config.h"
-#include "fh_error.h"
-
-struct fh_thread_s;
-struct fh_word_s;
-struct fh_instruction_s;
-
-/** Word handler typedef */
-typedef enum fh_error (*word_exec_t)(struct fh_thread_s *fh);
-
-/** Forth runtime global state */
-struct fh_global_s {
-  /** Verbose logging enabled */
-  bool verbose;
-  /** Interactive mode (i.e. not started with a file argument) */
-  bool interactive;
-};
-
-extern struct fh_global_s fh_globals;
-
-/* logging */
-#define LOG(format, ...) do { if(fh_globals.verbose) { fprintf(stderr, format "\n", ##__VA_ARGS__); } } while (0)
-#define LOGI(format, ...) fprintf(stderr, "\x1b[32m" format "\x1b[m\n", ##__VA_ARGS__)
-#define LOGE(format, ...) fprintf(stderr, "\x1b[31;1m" format "\x1b[m\n", ##__VA_ARGS__)
-/* Forth standard output. XXX should be stdout, but then colors get mangled if logging is used */
-#define FHPRINT(format, ...) fprintf(stderr, "\x1b[33;1m" format "\x1b[m", ##__VA_ARGS__)
-#define FHPRINT_SVC(format, ...) fprintf(stderr, "" format "", ##__VA_ARGS__)
-
-enum fh_error fh_init_thread(struct fh_thread_s *fh);
-enum fh_error fh_process_line(struct fh_thread_s *fh, char *linebuf);
-
-#endif //FORTH_H
diff --git a/fh_builtins.h b/include/fh_builtins.h
similarity index 100%
rename from fh_builtins.h
rename to include/fh_builtins.h
diff --git a/fh_config.h b/include/fh_config.h
similarity index 100%
rename from fh_config.h
rename to include/fh_config.h
diff --git a/fh_error.h b/include/fh_error.h
similarity index 100%
rename from fh_error.h
rename to include/fh_error.h
diff --git a/include/fh_globals.h b/include/fh_globals.h
new file mode 100644
index 0000000..17c8683
--- /dev/null
+++ b/include/fh_globals.h
@@ -0,0 +1,20 @@
+/**
+ * Global state
+ *
+ * Created on 2021/11/13.
+ */
+
+#ifndef FORTH_FH_GLOBALS_H
+#define FORTH_FH_GLOBALS_H
+
+/** Forth runtime global state */
+struct fh_global_s {
+  /** Verbose logging enabled */
+  bool verbose;
+  /** Interactive mode (i.e. not started with a file argument) */
+  bool interactive;
+};
+
+extern struct fh_global_s fh_globals;
+
+#endif //FORTH_FH_GLOBALS_H
diff --git a/fh_mem.h b/include/fh_mem.h
similarity index 100%
rename from fh_mem.h
rename to include/fh_mem.h
diff --git a/include/fh_print.h b/include/fh_print.h
new file mode 100644
index 0000000..61307ec
--- /dev/null
+++ b/include/fh_print.h
@@ -0,0 +1,24 @@
+/**
+ * Forth printing
+ *
+ * Created on 2021/11/13.
+ */
+
+#ifndef FORTH_FH_PRINT_H
+#define FORTH_FH_PRINT_H
+
+/* for printing */
+#include <stdlib.h>
+#include <stdio.h>
+#include "fh_globals.h"
+
+/* logging */
+#define LOG(format, ...) do { if(fh_globals.verbose) { fprintf(stderr, format "\n", ##__VA_ARGS__); } } while (0)
+#define LOGI(format, ...) fprintf(stderr, "\x1b[32m" format "\x1b[m\n", ##__VA_ARGS__)
+#define LOGE(format, ...) fprintf(stderr, "\x1b[31;1m" format "\x1b[m\n", ##__VA_ARGS__)
+
+/* Forth standard output. XXX should be stdout, but then colors get mangled if logging is used */
+#define FHPRINT(format, ...) fprintf(stderr, "\x1b[33;1m" format "\x1b[m", ##__VA_ARGS__)
+#define FHPRINT_SVC(format, ...) fprintf(stderr, "" format "", ##__VA_ARGS__)
+
+#endif //FORTH_FH_PRINT_H
diff --git a/fh_runtime.h b/include/fh_runtime.h
similarity index 95%
rename from fh_runtime.h
rename to include/fh_runtime.h
index 605116d..3db86f6 100644
--- a/fh_runtime.h
+++ b/include/fh_runtime.h
@@ -9,6 +9,17 @@
 
 #include <stdint.h>
 #include <stddef.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "fh_config.h"
+
+struct fh_word_s;
+struct fh_instruction_s;
+struct fh_thread_s;
+
+/** Word handler typedef */
+typedef enum fh_error (*word_exec_t)(struct fh_thread_s *fh);
 
 /** Bytecode instruction type marker */
 enum fb_instruction_kind {
diff --git a/fh_stack.h b/include/fh_stack.h
similarity index 93%
rename from fh_stack.h
rename to include/fh_stack.h
index f5f7584..e513de7 100644
--- a/fh_stack.h
+++ b/include/fh_stack.h
@@ -1,5 +1,5 @@
 /**
- * Forth internal stack operations
+ * Forth stack operations
  *
  * Created on 2021/11/13.
  */
diff --git a/include/forth.h b/include/forth.h
new file mode 100644
index 0000000..cd3af4b
--- /dev/null
+++ b/include/forth.h
@@ -0,0 +1,21 @@
+/**
+ * Forth main entry-point
+ *
+ * Created on 2021/11/13.
+ */
+
+#ifndef FORTH_H
+#define FORTH_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "fh_config.h"
+#include "fh_error.h"
+
+struct fh_thread_s;
+
+enum fh_error fh_init(struct fh_thread_s *fh);
+enum fh_error fh_process_line(struct fh_thread_s *fh, const char *linebuf);
+
+#endif //FORTH_H
diff --git a/fh_builtins.c b/src/fh_builtins.c
similarity index 97%
rename from fh_builtins.c
rename to src/fh_builtins.c
index 7a08955..9c00a65 100644
--- a/fh_builtins.c
+++ b/src/fh_builtins.c
@@ -1,6 +1,9 @@
 #include <string.h>
-#include "forth.h"
+#include <stdbool.h>
 #include "fh_runtime.h"
+#include "fh_config.h"
+#include "fh_error.h"
+#include "fh_print.h"
 #include "fh_builtins.h"
 #include "fh_stack.h"
 #include "fh_mem.h"
diff --git a/fh_mem.c b/src/fh_mem.c
similarity index 100%
rename from fh_mem.c
rename to src/fh_mem.c
diff --git a/fh_runtime.c b/src/fh_runtime.c
similarity index 97%
rename from fh_runtime.c
rename to src/fh_runtime.c
index 3d4cb39..6c03b16 100644
--- a/fh_runtime.c
+++ b/src/fh_runtime.c
@@ -1,11 +1,14 @@
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+
 #include "forth.h"
 #include "fh_runtime.h"
 #include "fh_builtins.h"
 #include "fh_stack.h"
 #include "fh_mem.h"
-#include <string.h>
-#include <errno.h>
-#include <ctype.h>
+#include "fh_globals.h"
+#include "fh_print.h"
 
 struct fh_global_s fh_globals = {};
 
@@ -168,7 +171,7 @@ enum fh_error w_user_word(struct fh_thread_s *fh)
 
 
 /** Initialize a runtime */
-enum fh_error fh_init_thread(struct fh_thread_s *fh)
+enum fh_error fh_init(struct fh_thread_s *fh)
 {
   enum fh_error rv;
 
@@ -184,7 +187,7 @@ enum fh_error fh_init_thread(struct fh_thread_s *fh)
 /** Process a quoted string read from input */
 static enum fh_error fh_handle_quoted_string(
     struct fh_thread_s *fh,
-    char *start,
+    const char *start,
     size_t len
 )
 {
@@ -229,7 +232,7 @@ static enum fh_error fh_handle_quoted_string(
 /** Process a word read from input */
 static enum fh_error fh_handle_word(
     struct fh_thread_s *fh,
-    char *start,
+    const char *start,
     size_t len
 )
 {
@@ -291,10 +294,10 @@ static inline bool isnl(char c)
 }
 
 /** Process a line read from input */
-enum fh_error fh_process_line(struct fh_thread_s *fh, char *linebuf)
+enum fh_error fh_process_line(struct fh_thread_s *fh, const char *linebuf)
 {
   enum fh_error rv;
-  char *rp = linebuf;
+  const char *rp = linebuf;
   char c;
 
   if (!fh_globals.interactive) {
diff --git a/fh_stack.c b/src/fh_stack.c
similarity index 96%
rename from fh_stack.c
rename to src/fh_stack.c
index 1898550..aa2de25 100644
--- a/fh_stack.c
+++ b/src/fh_stack.c
@@ -1,6 +1,8 @@
-#include "forth.h"
+#include "fh_error.h"
+#include "fh_config.h"
 #include "fh_runtime.h"
 #include "fh_stack.h"
+#include "fh_print.h"
 
 /** Pop from data stack */
 enum fh_error ds_pop(struct fh_thread_s *fh, uint32_t *out)
diff --git a/main.c b/src/main.c
similarity index 95%
rename from main.c
rename to src/main.c
index df7b18d..e376bc4 100644
--- a/main.c
+++ b/src/main.c
@@ -1,20 +1,18 @@
 #include <stdio.h>
-#include <stdint.h>
 #include <stdbool.h>
-#include <stdlib.h>
 #include <string.h>
-#include <errno.h>
 #include <unistd.h>
 #include <ctype.h>
 
 #include "forth.h"
 #include "fh_runtime.h"
+#include "fh_print.h"
 
 int main(int argc, char *argv[])
 {
   enum fh_error rv;
   struct fh_thread_s fh;
-  rv = fh_init_thread(&fh);
+  rv = fh_init(&fh);
   if (rv != FH_OK) {
     LOGE("Error in forth init: %s", fherr_name(rv));
     return 1;