diff --git a/Makefile b/Makefile
index cc6d976..4f5004d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,16 +1,16 @@
 .POSIX:
 .SUFFIXES:
 
-VERSION = 1.0
+VERSION = "1.0"
 TARGET = 90s
 MANPAGE = $(TARGET).1
 PREFIX ?= /usr/local
 BINDIR = $(PREFIX)/bin
 MANDIR = $(PREFIX)/share/man/man1
 
-CFLAGS = -O3 -march=native -mtune=native -pipe -s -flto -std=c99 -pedantic -Wall -DVERSION=$(VERSION)
+CFLAGS = -Os -march=native -mtune=native -pipe -s -flto -std=c99 -pedantic -Wall -DVERSION=$(VERSION) -D_DEFAULT_SOURCE
 
-SRC = src/*.c
+SRC != find src -name *.c
 INCLUDE = include
 
 $(TARGET): $(SRC)
diff --git a/include/commands.h b/include/commands.h
index 0621168..4c5d8ac 100644
--- a/include/commands.h
+++ b/include/commands.h
@@ -2,7 +2,7 @@
 #define COMMANDS_H_
 
 char *replace_absolute_home(char *str);
-int num_builtins();
+int num_builtins(void);
 bool is_builtin(char *command);
 int execute(char **args, int fd, int options);
 int execute_pipe(char ***args);
diff --git a/include/history.h b/include/history.h
index 83f5aa1..45b69bf 100644
--- a/include/history.h
+++ b/include/history.h
@@ -4,7 +4,7 @@
 extern int cmd_count;
 
 void save_command_history(char *args);
-void check_history_file();
+void check_history_file(void);
 char *read_command(int direction);
 char **get_all_history(bool check);
 
diff --git a/src/90s.c b/src/90s.c
index c3add9d..f5b8c1c 100644
--- a/src/90s.c
+++ b/src/90s.c
@@ -35,7 +35,7 @@ void change_terminal_attribute(int option) {
     }
 }  
 
-char **setup_path_variable() {
+char **setup_path_variable(void) {
     char *envpath = getenv("PATH");
     if (envpath == NULL) {
         fprintf(stderr, "90s: PATH environment variable is missing\n");
@@ -95,7 +95,7 @@ void shiftright(int chars) {
     printf("\033[%dC", chars);
 }
 
-void clearline() {
+void clearline(void) {
     printf("\033[K"); // clear line to the right of cursor
 }
 
diff --git a/src/commands.c b/src/commands.c
index 5941c02..637ced7 100644
--- a/src/commands.c
+++ b/src/commands.c
@@ -58,7 +58,7 @@ char *shortcut_expand_dirs[] = {
     "/usr/local/bin",
 };
 
-char *gethome() {
+char *gethome(void) {
     char *home = getenv("HOME");
     if (home == NULL) {
         fprintf(stderr, "Error: HOME environment variable not set.\n");
@@ -118,7 +118,7 @@ char *replace_absolute_home(char *str) {
 }
 
 // number of built in commands
-int num_builtins() {
+int num_builtins(void) {
     return sizeof(builtin_cmds) / sizeof(char *);
 }
 
diff --git a/src/history.c b/src/history.c
index 709ba13..6756964 100644
--- a/src/history.c
+++ b/src/history.c
@@ -21,7 +21,7 @@ FILE *open_history_file(char *mode) {
     }
     return history_file;
 }
-void check_history_file() {
+void check_history_file(void) {
     char *env_home;
     env_home = getenv("XDG_CONFIG_HOME");
     if (env_home == NULL) {
diff --git a/src/job.c b/src/job.c
index 5fc0bc4..0ac6a74 100644
--- a/src/job.c
+++ b/src/job.c
@@ -13,7 +13,7 @@ typedef struct job {
 
 job *jobs = NULL;
 
-int num_jobs() {
+int num_jobs(void) {
     job *current = jobs;
     int count = 0;
     while (current != NULL) {