diff --git a/st.c b/st.c
index 09ffd68..8d13d58 100644
--- a/st.c
+++ b/st.c
@@ -200,17 +200,17 @@ static void tscrolldown(int, int, int);
 static void tscrollup(int, int);
 static void tscrolldown(int, int);
 #endif // SCROLLBACK_PATCH
-static void tsetattr(int *, int);
-static void tsetchar(Rune, Glyph *, int, int);
+static void tsetattr(const int *, int);
+static void tsetchar(Rune, const Glyph *, int, int);
 static void tsetdirt(int, int);
 static void tsetscroll(int, int);
 static void tswapscreen(void);
-static void tsetmode(int, int, int *, int);
+static void tsetmode(int, int, const int *, int);
 static int twrite(const char *, int, int);
 static void tcontrolcode(uchar );
 static void tdectest(char );
 static void tdefutf8(char);
-static int32_t tdefcolor(int *, int *, int);
+static int32_t tdefcolor(const int *, int *, int);
 static void tdeftran(char);
 static void tstrsequence(uchar);
 static void selnormalize(void);
@@ -243,10 +243,10 @@ static pid_t pid;
 sixel_state_t sixel_st;
 #endif // SIXEL_PATCH
 
-static uchar utfbyte[UTF_SIZ + 1] = {0x80,    0, 0xC0, 0xE0, 0xF0};
-static uchar utfmask[UTF_SIZ + 1] = {0xC0, 0x80, 0xE0, 0xF0, 0xF8};
-static Rune utfmin[UTF_SIZ + 1] = {       0,    0,  0x80,  0x800,  0x10000};
-static Rune utfmax[UTF_SIZ + 1] = {0x10FFFF, 0x7F, 0x7FF, 0xFFFF, 0x10FFFF};
+static const uchar utfbyte[UTF_SIZ + 1] = {0x80,    0, 0xC0, 0xE0, 0xF0};
+static const uchar utfmask[UTF_SIZ + 1] = {0xC0, 0x80, 0xE0, 0xF0, 0xF8};
+static const Rune utfmin[UTF_SIZ + 1] = {       0,    0,  0x80,  0x800,  0x10000};
+static const Rune utfmax[UTF_SIZ + 1] = {0x10FFFF, 0x7F, 0x7FF, 0xFFFF, 0x10FFFF};
 
 #if VIM_BROWSE_PATCH
 int buffCols;
@@ -298,12 +298,13 @@ xrealloc(void *p, size_t len)
 }
 
 char *
-xstrdup(char *s)
+xstrdup(const char *s)
 {
-	if ((s = strdup(s)) == NULL)
+	char *p;
+	if ((p = strdup(s)) == NULL)
 		die("strdup: %s\n", strerror(errno));
 
-	return s;
+	return p;
 }
 
 size_t
@@ -694,7 +695,7 @@ selsnap(int *x, int *y, int direction)
 {
 	int newx, newy, xt, yt;
 	int delim, prevdelim;
-	Glyph *gp, *prevgp;
+	const Glyph *gp, *prevgp;
 
 	switch (sel.snap) {
 	case SNAP_WORD:
@@ -792,7 +793,7 @@ getsel(void)
 	#else
 	int y, bufsize, lastx, linelen;
 	#endif // VIM_BROWSE_PATCH
-	Glyph *gp, *last;
+	const Glyph *gp, *last;
 
 	if (sel.ob.x == -1)
 		return NULL;
@@ -1032,7 +1033,7 @@ stty(char **args)
 }
 
 int
-ttynew(char *line, char *cmd, char *out, char **args)
+ttynew(const char *line, char *cmd, const char *out, char **args)
 {
 	int m, s;
 	#if EXTERNALPIPEIN_PATCH && EXTERNALPIPE_PATCH
@@ -1611,9 +1612,9 @@ tmoveto(int x, int y)
 }
 
 void
-tsetchar(Rune u, Glyph *attr, int x, int y)
+tsetchar(Rune u, const Glyph *attr, int x, int y)
 {
-	static char *vt100_0[62] = { /* 0x41 - 0x7e */
+	static const char *vt100_0[62] = { /* 0x41 - 0x7e */
 		"↑", "↓", "→", "←", "█", "▚", "☃", /* A - G */
 		0, 0, 0, 0, 0, 0, 0, 0, /* H - O */
 		0, 0, 0, 0, 0, 0, 0, 0, /* P - W */
@@ -1743,7 +1744,7 @@ tdeleteline(int n)
 }
 
 int32_t
-tdefcolor(int *attr, int *npar, int l)
+tdefcolor(const int *attr, int *npar, int l)
 {
 	int32_t idx = -1;
 	uint r, g, b;
@@ -1793,7 +1794,7 @@ tdefcolor(int *attr, int *npar, int l)
 }
 
 void
-tsetattr(int *attr, int l)
+tsetattr(const int *attr, int l)
 {
 	int i;
 	int32_t idx;
@@ -1966,9 +1967,10 @@ tsetscroll(int t, int b)
 }
 
 void
-tsetmode(int priv, int set, int *args, int narg)
+tsetmode(int priv, int set, const int *args, int narg)
 {
-	int alt, *lim;
+	int alt;
+	const int *lim;
 
 	for (lim = args + narg; args < lim; ++args) {
 		if (priv) {
@@ -2616,7 +2618,7 @@ void
 tdumpline(int n)
 {
 	char buf[UTF_SIZ];
-	Glyph *bp, *end;
+	const Glyph *bp, *end;
 
 	bp = &term.line[n][0];
 	end = &bp[MIN(tlinelen(n), term.col) - 1];
diff --git a/st.h b/st.h
index 3844907..92db4c9 100644
--- a/st.h
+++ b/st.h
@@ -303,7 +303,7 @@ void tmoveto(int x, int y);
 #endif // VIM_BROWSE_PATCH
 void tsetdirtattr(int);
 void ttyhangup(void);
-int ttynew(char *, char *, char *, char **);
+int ttynew(const char *, char *, const char *, char **);
 size_t ttyread(void);
 void ttyresize(int, int);
 void ttywrite(const char *, size_t, int);
@@ -321,7 +321,7 @@ size_t utf8encode(Rune, char *);
 
 void *xmalloc(size_t);
 void *xrealloc(void *, size_t);
-char *xstrdup(char *);
+char *xstrdup(const char *);
 #if BOXDRAW_PATCH
 int isboxdraw(Rune);
 ushort boxdrawindex(const Glyph *);
diff --git a/x.c b/x.c
index 91e6567..6c6aaac 100644
--- a/x.c
+++ b/x.c
@@ -78,7 +78,7 @@ static void xresize(int, int);
 static void xhints(void);
 static int xloadcolor(int, const char *, Color *);
 static int xloadfont(Font *, FcPattern *);
-static void xloadfonts(char *, double);
+static void xloadfonts(const char *, double);
 static void xunloadfont(Font *);
 static void xunloadfonts(void);
 static void xsetenv(void);
@@ -1141,7 +1141,7 @@ xloadfont(Font *f, FcPattern *pattern)
 }
 
 void
-xloadfonts(char *fontstr, double fontsize)
+xloadfonts(const char *fontstr, double fontsize)
 {
 	FcPattern *pattern;
 	double fontval;
@@ -1149,7 +1149,7 @@ xloadfonts(char *fontstr, double fontsize)
 	if (fontstr[0] == '-')
 		pattern = XftXlfdParse(fontstr, False, False);
 	else
-		pattern = FcNameParse((FcChar8 *)fontstr);
+		pattern = FcNameParse((const FcChar8 *)fontstr);
 
 	if (!pattern)
 		die("can't open font %s\n", fontstr);