diff --git a/qrexec-lib/buffer.c b/qrexec-lib/buffer.c
index f0be787..12bc4eb 100644
--- a/qrexec-lib/buffer.c
+++ b/qrexec-lib/buffer.c
@@ -67,7 +67,7 @@ Yet the profiling output show they are not significant CPU hogs, so
 we keep them so simple to make them obviously correct.
 */
 
-void buffer_append(struct buffer *b, char *data, int len)
+void buffer_append(struct buffer *b, const char *data, int len)
 {
 	int newsize;
 	char *qdata;
diff --git a/qrexec-lib/exec.c b/qrexec-lib/exec.c
index a87f505..b593af8 100644
--- a/qrexec-lib/exec.c
+++ b/qrexec-lib/exec.c
@@ -23,7 +23,7 @@
 #include <unistd.h>
 #include <stdio.h>
 
-extern void do_exec(char *);
+extern void do_exec(const char *);
 
 void fix_fds(int fdin, int fdout, int fderr)
 {
@@ -40,7 +40,7 @@ void fix_fds(int fdin, int fdout, int fderr)
 		close(fderr);
 }
 
-void do_fork_exec(char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
+void do_fork_exec(const char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
 		  int *stderr_fd)
 {
 	int inpipe[2], outpipe[2], errpipe[2];
diff --git a/qrexec-lib/ioall.c b/qrexec-lib/ioall.c
index 2a81df4..ac679a8 100644
--- a/qrexec-lib/ioall.c
+++ b/qrexec-lib/ioall.c
@@ -25,7 +25,7 @@
 #include <fcntl.h>
 #include <errno.h>
 
-void perror_wrapper(char * msg)
+void perror_wrapper(const char * msg)
 {
 	int prev=errno;
 	perror(msg);
@@ -44,7 +44,7 @@ void set_block(int fd)
 	fcntl(fd, F_SETFL, fl & ~O_NONBLOCK);
 }
 
-int write_all(int fd, void *buf, int size)
+int write_all(int fd, const void *buf, int size)
 {
 	int written = 0;
 	int ret;
diff --git a/qrexec-lib/ioall.h b/qrexec-lib/ioall.h
index c9913e8..c822bbe 100644
--- a/qrexec-lib/ioall.h
+++ b/qrexec-lib/ioall.h
@@ -1,4 +1,4 @@
-int write_all(int fd, void *buf, int size);
+int write_all(int fd, const void *buf, int size);
 int read_all(int fd, void *buf, int size);
 int copy_fd_all(int fdout, int fdin);
 void set_nonblock(int fd);
diff --git a/qrexec-lib/libqrexec-utils.h b/qrexec-lib/libqrexec-utils.h
index 96095cf..b090569 100644
--- a/qrexec-lib/libqrexec-utils.h
+++ b/qrexec-lib/libqrexec-utils.h
@@ -29,28 +29,28 @@ struct buffer {
 
 void buffer_init(struct buffer *b);
 void buffer_free(struct buffer *b);
-void buffer_append(struct buffer *b, char *data, int len);
+void buffer_append(struct buffer *b, const char *data, int len);
 void buffer_remove(struct buffer *b, int len);
 int buffer_len(struct buffer *b);
 void *buffer_data(struct buffer *b);
 
 
-void do_fork_exec(char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
+void do_fork_exec(const char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
 		  int *stderr_fd);
 int peer_server_init(int port);
 char *peer_client_init(int dom, int port);
 void wait_for_vchan_or_argfd(int max, fd_set * rdset, fd_set * wrset);
-int read_ready_vchan_ext();
+int read_ready_vchan_ext(void);
 int read_all(int fd, void *buf, int size);
 int read_all_vchan_ext(void *buf, int size);
-int write_all(int fd, void *buf, int size);
+int write_all(int fd, const void *buf, int size);
 int write_all_vchan_ext(void *buf, int size);
-int buffer_space_vchan_ext();
+int buffer_space_vchan_ext(void);
 void fix_fds(int fdin, int fdout, int fderr);
 void set_nonblock(int fd);
 void set_block(int fd);
 
-int get_server_socket(char *);
+int get_server_socket(const char *);
 int do_accept(int s);
 
 enum {
@@ -60,7 +60,7 @@ enum {
 };
 
 int flush_client_data(int fd, int client_id, struct buffer *buffer);
-int write_stdin(int fd, int client_id, char *data, int len,
+int write_stdin(int fd, int client_id, const char *data, int len,
 		struct buffer *buffer);
 void set_nonblock(int fd);
 int fork_and_flush_stdin(int fd, struct buffer *buffer);
diff --git a/qrexec-lib/libqubes-rpc-filecopy.h b/qrexec-lib/libqubes-rpc-filecopy.h
index fcf58e7..8f57728 100644
--- a/qrexec-lib/libqubes-rpc-filecopy.h
+++ b/qrexec-lib/libqubes-rpc-filecopy.h
@@ -64,7 +64,7 @@ int copy_file(int outfd, int infd, long long size, unsigned long *crc32);
 char *copy_file_status_to_str(int status);
 void set_size_limit(long long new_bytes_limit, long long new_files_limit);
 void set_verbose(int value);
-int write_all(int fd, void *buf, int size);
+int write_all(int fd, const void *buf, int size);
 int read_all(int fd, void *buf, int size);
 int copy_fd_all(int fdout, int fdin);
 void set_nonblock(int fd);
@@ -73,6 +73,6 @@ void set_block(int fd);
 extern unsigned long Crc32_ComputeBuf( unsigned long inCrc32, const void *buf,
         size_t bufLen );
 
-extern int do_unpack();
+extern int do_unpack(void);
 
 #endif /* _LIBQUBES_RPC_FILECOPY_H */
diff --git a/qrexec-lib/unix-server.c b/qrexec-lib/unix-server.c
index 8be6e1a..7a3512c 100644
--- a/qrexec-lib/unix-server.c
+++ b/qrexec-lib/unix-server.c
@@ -27,7 +27,7 @@
 #include <stdlib.h>
 //#include "qrexec.h"
 
-int get_server_socket(char *socket_address)
+int get_server_socket(const char *socket_address)
 {
 	struct sockaddr_un sockname;
 	int s;
diff --git a/qrexec-lib/unpack.c b/qrexec-lib/unpack.c
index 38bf270..696ca93 100644
--- a/qrexec-lib/unpack.c
+++ b/qrexec-lib/unpack.c
@@ -38,7 +38,7 @@ int read_all_with_crc(int fd, void *buf, int size) {
 	return ret;
 }
 
-void send_status_and_crc(int code, char *last_filename) {
+void send_status_and_crc(int code, const char *last_filename) {
 	struct result_header hdr;
 	struct result_header_ext hdr_ext;
 	int saved_errno;
@@ -58,7 +58,7 @@ void send_status_and_crc(int code, char *last_filename) {
 	errno = saved_errno;
 }
 
-void do_exit(int code, char *last_filename)
+void do_exit(int code, const char *last_filename)
 {
 	close(0);
 	send_status_and_crc(code, last_filename);
@@ -66,7 +66,7 @@ void do_exit(int code, char *last_filename)
 }
 
 void fix_times_and_perms(struct file_header *untrusted_hdr,
-			 char *untrusted_name)
+			 const char *untrusted_name)
 {
 	struct timeval times[2] =
 	    { {untrusted_hdr->atime, untrusted_hdr->atime_nsec / 1000},
@@ -82,7 +82,7 @@ void fix_times_and_perms(struct file_header *untrusted_hdr,
 
 
 void process_one_file_reg(struct file_header *untrusted_hdr,
-			  char *untrusted_name)
+			  const char *untrusted_name)
 {
 	int ret;
 	int fdout = open(untrusted_name, O_WRONLY | O_CREAT | O_EXCL | O_NOFOLLOW, 0700);	/* safe because of chroot */
@@ -105,7 +105,7 @@ void process_one_file_reg(struct file_header *untrusted_hdr,
 
 
 void process_one_file_dir(struct file_header *untrusted_hdr,
-			  char *untrusted_name)
+			  const char *untrusted_name)
 {
 // fix perms only when the directory is sent for the second time
 // it allows to transfer r.x directory contents, as we create it rwx initially
@@ -122,7 +122,7 @@ void process_one_file_dir(struct file_header *untrusted_hdr,
 }
 
 void process_one_file_link(struct file_header *untrusted_hdr,
-			   char *untrusted_name)
+			   const char *untrusted_name)
 {
 	char untrusted_content[MAX_PATH_LENGTH];
 	unsigned int filelen;
@@ -161,7 +161,7 @@ void process_one_file(struct file_header *untrusted_hdr)
 		fprintf(stderr, "%s\n", untrusted_namebuf);
 }
 
-int do_unpack()
+int do_unpack(void)
 {
 	struct file_header untrusted_hdr;
 	total_bytes = total_files = 0;
diff --git a/qrexec-lib/write-stdin.c b/qrexec-lib/write-stdin.c
index 8447de8..40a18c1 100644
--- a/qrexec-lib/write-stdin.c
+++ b/qrexec-lib/write-stdin.c
@@ -69,7 +69,7 @@ Write "len" bytes from "data" to "fd". If not all written, buffer the rest
 to "buffer", and notify the peer that the client "client_id" pipe is full via 
 MSG_XOFF message.
 */
-int write_stdin(int fd, int client_id, char *data, int len,
+int write_stdin(int fd, int client_id, const char *data, int len,
 		struct buffer *buffer)
 {
 	int ret;