diff --git a/src/libs/libdriver/input.cpp b/src/libs/libdriver/input.cpp
index 15f0ef1c..f49721eb 100644
--- a/src/libs/libdriver/input.cpp
+++ b/src/libs/libdriver/input.cpp
@@ -383,7 +383,8 @@ ColorArg color_from_Df_command(IntArg);
 void delete_current_env(void);	// delete global var current_env
 void fatal_command(char);	// abort for invalid command
 inline Char get_char(void);	// read next character from input stream
-ColorArg get_color_arg(void);	// read in argument for new color cmds
+ColorArg get_color_arg(const char * cmd);
+				// read in argument for new color cmds
 IntArray *get_D_fixed_args(const size_t);
 				// read in fixed number of integer
 				// arguments
@@ -393,13 +394,16 @@ IntArray *get_D_fixed_args_odd_dummy(const size_t);
 IntArray *get_D_variable_args(void);
                                 // variable, even number of int args
 char *get_extended_arg(void);	// argument for 'x X' (several lines)
-IntArg get_integer_arg(void);	// read in next integer argument
+IntArg get_integer_arg(const char * const);
+				// read in next integer argument
 IntArray *get_possibly_integer_args();
 				// 0 or more integer arguments
-char *get_string_arg(void);	// read in next string arg, ended by WS
+char *get_string_arg(const char * const);
+				// read in next string arg, ended by WS
 inline bool is_space_or_tab(const Char);
 				// test on space/tab char
-Char next_arg_begin(void);	// skip white space on current line
+Char next_arg_begin(const char * const);
+				// skip white space on current line
 Char next_command(void);	// go to next command, evt. diff. line
 inline bool odd(const int);	// test if integer is odd
 void position_to_end_of_args(const IntArray * const);
@@ -631,12 +635,15 @@ get_char(void)
 /* get_color_arg():
    Retrieve an argument suitable for the color commands m and DF.
 
+   cmd: In parameter; command whose argument we're parsing.  To be
+        passed to next_arg_begin().
+
    Return: The retrieved color argument.
 */
 ColorArg
-get_color_arg(void)
+get_color_arg(const char * const cmd)
 {
-  IntArg x = get_integer_arg();
+  IntArg x = get_integer_arg(cmd);
   if (x < 0 || x > (IntArg)COLORARG_MAX) {
     error("color component argument out of range");
     x = 0;
@@ -662,12 +669,20 @@ get_color_arg(void)
 IntArray *
 get_D_fixed_args(const size_t number)
 {
+  // Set up command argument buffer template for diagnostics.
+  char cmdbuft[] = "D (argument 18446744073709551616)"; // 2^64
+  char *cmdbuf = (char *)calloc(1, strlen(cmdbuft));
   if (number <= 0)
     fatal("requested number of arguments must be > 0");
   IntArray *args = new IntArray(number);
-  for (size_t i = 0; i < number; i++)
-    args->append(get_integer_arg());
+  for (size_t i = 0; i < number; i++) {
+    if (0 == sprintf(cmdbuf, "D (argument %ld)", number))
+	error("internal error using sprintf() on command buffer");
+    else
+      args->append(get_integer_arg(cmdbuf));
+  }
   skip_line_D();
+  free(cmdbuf);
   return args;
 }
 
@@ -688,11 +703,17 @@ get_D_fixed_args(const size_t number)
 IntArray *
 get_D_fixed_args_odd_dummy(const size_t number)
 {
+  // Set up command argument buffer template for diagnostics.
+  char cmdbuft[] = "D (argument 18446744073709551616)"; // 2^64
+  char *cmdbuf = (char *)calloc(1, strlen(cmdbuft));
   if (number <= 0)
     fatal("requested number of arguments must be > 0");
   IntArray *args = new IntArray(number);
   for (size_t i = 0; i < number; i++)
-    args->append(get_integer_arg());
+    if (0 == sprintf(cmdbuf, "D (argument %ld)", number))
+	error("internal error using sprintf() on command buffer");
+    else
+      args->append(get_integer_arg(cmdbuf));
   if (odd(number)) {
     IntArray *a = get_possibly_integer_args();
     if (a->len() > 1)
@@ -700,6 +721,7 @@ get_D_fixed_args_odd_dummy(const size_t number)
     delete a;
   }
   skip_line_D();
+  free(cmdbuf);
   return args;
 }
 
@@ -746,7 +768,7 @@ char *
 get_extended_arg(void)
 {
   StringBuf buf = StringBuf();
-  Char c = next_arg_begin();
+  Char c = next_arg_begin("x X");
   while ((int) c != EOF) {
     if ((int) c == '\n') {
       current_lineno++;
@@ -774,13 +796,16 @@ get_extended_arg(void)
 
    Fatal error on all other situations.
 
+   cmd: In parameter; command whose argument we're parsing.  To be
+        passed to next_arg_begin().
+
    Return: Retrieved integer.
 */
 IntArg
-get_integer_arg(void)
+get_integer_arg(const char * const cmd)
 {
   StringBuf buf = StringBuf();
-  Char c = next_arg_begin();
+  Char c = next_arg_begin(cmd);
   if ((int) c == '-') {
     buf.append(c);
     c = get_char();
@@ -892,13 +917,16 @@ get_possibly_integer_args()
    - The terminating space, tab, newline, or EOF character is restored
      onto the input queue, so no line skip.
 
+   cmd: In parameter; command whose argument we're parsing.  To be
+        passed to next_arg_begin().
+
    Return: Retrieved string as char *, allocated by 'new'.
 */
 char *
-get_string_arg(void)
+get_string_arg(const char * const cmd)
 {
   StringBuf buf = StringBuf();
-  Char c = next_arg_begin();
+  Char c = next_arg_begin(cmd);
   while (!is_space_or_tab(c)
 	 && c != Char('\n') && c != Char(EOF)) {
     buf.append(c);
@@ -928,10 +956,13 @@ is_space_or_tab(const Char c)
 
    Skip space and tab characters; error on newline or EOF.
 
+   cmd: In parameter, name of command whose argument we're gathering, so
+        that our diagnostic message is useful.
+
    Return: The first character different from these (including '#').
 */
 Char
-next_arg_begin(void)
+next_arg_begin(const char * const cmd)
 {
   Char c;
   while (1) {
@@ -942,7 +973,7 @@ next_arg_begin(void)
       break;
     case '\n':
     case EOF:
-      error("missing argument");
+      error("missing argument to %1 command", cmd);
       return c;
     default:			// first essential character
       return c;
@@ -1260,39 +1291,42 @@ unget_char(const Char c)
 
    col: In-out-parameter; the color object to be set, must have
         been initialized before.
+
+   cmd: In parameter; command whose argument we're parsing.  To be
+        passed to next_arg_begin().
 */
 void
-parse_color_command(color *col)
+parse_color_command(color *col, const char * const cmd)
 {
   ColorArg gray = 0;
   ColorArg red = 0, green = 0, blue = 0;
   ColorArg cyan = 0, magenta = 0, yellow = 0, black = 0;
-  Char subcmd = next_arg_begin();
+  Char subcmd = next_arg_begin(cmd);
   switch((int) subcmd) {
   case 'c':			// DFc or mc: CMY
-    cyan = get_color_arg();
-    magenta = get_color_arg();
-    yellow = get_color_arg();
+    cyan = get_color_arg(cmd);
+    magenta = get_color_arg(cmd);
+    yellow = get_color_arg(cmd);
     col->set_cmy(cyan, magenta, yellow);
     break;
   case 'd':			// DFd or md: set default color
     col->set_default();
     break;
   case 'g':			// DFg or mg: gray
-    gray = get_color_arg();
+    gray = get_color_arg(cmd);
     col->set_gray(gray);
     break;
   case 'k':			// DFk or mk: CMYK
-    cyan = get_color_arg();
-    magenta = get_color_arg();
-    yellow = get_color_arg();
-    black = get_color_arg();
+    cyan = get_color_arg(cmd);
+    magenta = get_color_arg(cmd);
+    yellow = get_color_arg(cmd);
+    black = get_color_arg(cmd);
     col->set_cmyk(cyan, magenta, yellow, black);
     break;
   case 'r':			// DFr or mr: RGB
-    red = get_color_arg();
-    green = get_color_arg();
-    blue = get_color_arg();
+    red = get_color_arg(cmd);
+    green = get_color_arg(cmd);
+    blue = get_color_arg(cmd);
     col->set_rgb(red, green, blue);
     break;
   default:
@@ -1314,7 +1348,7 @@ parse_color_command(color *col)
 void
 parse_D_command()
 {
-  Char subcmd = next_arg_begin();
+  Char subcmd = next_arg_begin("D");
   switch((int) subcmd) {
   case '~':			// D~: draw B-spline
     // actually, this isn't available for some postprocessors
@@ -1365,7 +1399,7 @@ parse_D_command()
     }
   case 'f':			// Df: set fill gray; obsoleted by DFg
     {
-      IntArg arg = get_integer_arg();
+      IntArg arg = get_integer_arg("Df");
       if ((arg >= 0) && (arg <= 1000)) {
 	// convert arg and treat it like DFg
 	ColorArg gray = color_from_Df_command(arg);
@@ -1378,7 +1412,7 @@ parse_D_command()
       }
       pr->change_fill_color(current_env);
       // skip unused 'vertical' component (\D'...' always emits pairs)
-      (void) get_integer_arg();
+      (void) get_integer_arg("Df (unused vertical)");
 #   ifdef STUPID_DRAWING_POSITIONING
       current_env->hpos += arg;
 #   endif
@@ -1386,7 +1420,7 @@ parse_D_command()
       break;
     }
   case 'F':			// DF: set fill color, several formats
-    parse_color_command(current_env->fill);
+    parse_color_command(current_env->fill, "DF");
     pr->change_fill_color(current_env);
     // no positioning (setting-only command)
     skip_line_x();
@@ -1448,13 +1482,13 @@ bool
 parse_x_command(void)
 {
   bool stopped = false;
-  char *subcmd_str = get_string_arg();
+  char *subcmd_str = get_string_arg("x");
   char subcmd = subcmd_str[0];
   switch (subcmd) {
   case 'f':			// x font: mount font
     {
-      IntArg n = get_integer_arg();
-      char *name = get_string_arg();
+      IntArg n = get_integer_arg("x f");
+      char *name = get_string_arg("x f");
       pr->load_font(n, name);
       a_delete name;
       skip_line_x();
@@ -1472,7 +1506,7 @@ parse_x_command(void)
       break;
     }
   case 'H':			// x Height: set character height
-    current_env->height = get_integer_arg();
+    current_env->height = get_integer_arg("x H");
     if (current_env->height == current_env->size)
       current_env->height = 0;
     skip_line_x();
@@ -1493,7 +1527,7 @@ parse_x_command(void)
     skip_line_x();
     break;
   case 'S':			// x Slant: set slant
-    current_env->slant = get_integer_arg();
+    current_env->slant = get_integer_arg("x S");
     skip_line_x();
     break;
   case 't':			// x trailer: generate trailer info
@@ -1505,7 +1539,7 @@ parse_x_command(void)
     break;
   case 'u':			// x underline: from .cu
     {
-      char *str_arg = get_string_arg();
+      char *str_arg = get_string_arg("x u");
       pr->special(str_arg, current_env, 'u');
       a_delete str_arg;
       skip_line_x();
@@ -1594,11 +1628,11 @@ do_file(const char *filename)
       return;
     if ((int) command != 'x')
       fatal("the first command must be 'x T'");
-    str_arg = get_string_arg();
+    str_arg = get_string_arg("x T");
     if (str_arg[0] != 'T')
       fatal("the first command must be 'x T'");
     a_delete str_arg;
-    char *tmp_dev = get_string_arg();
+    char *tmp_dev = get_string_arg("x T");
     if (pr == 0) {		// note: 'pr' initialized after prologue
       device = tmp_dev;
       if (!font::load_desc())
@@ -1616,18 +1650,18 @@ do_file(const char *filename)
     command = next_command();
     if ((int) command != 'x')
       fatal("the second command must be 'x res'");
-    str_arg = get_string_arg();
+    str_arg = get_string_arg("x res");
     if (str_arg[0] != 'r')
       fatal("the second command must be 'x res'");
     a_delete str_arg;
-    int_arg = get_integer_arg();
+    int_arg = get_integer_arg("x res (font)");
     EnvInt font_res = font::res;
     if (int_arg != font_res)
       fatal("resolution does not match");
-    int_arg = get_integer_arg();
+    int_arg = get_integer_arg("x res (hor)");
     if (int_arg != font::hor)
       fatal("minimum horizontal motion does not match");
-    int_arg = get_integer_arg();
+    int_arg = get_integer_arg("x res (vert)");
     if (int_arg != font::vert)
       fatal("minimum vertical motion does not match");
     skip_line_x();		// ignore further arguments
@@ -1636,7 +1670,7 @@ do_file(const char *filename)
     command = next_command();
     if (command != 'x')
       fatal("the third command must be 'x init'");
-    str_arg = get_string_arg();
+    str_arg = get_string_arg("x init");
     if (str_arg[0] != 'i')
       fatal("the third command must be 'x init'");
     a_delete str_arg;
@@ -1676,7 +1710,7 @@ do_file(const char *filename)
     case '9':
       {				// expect 2 digits and a character
 	char s[3];
-	Char c = next_arg_begin();
+	Char c = next_arg_begin("jump-and-move (digits)");
 	if (npages <= 0)
 	  fatal_command(command);
 	if (!isdigit((int) c)) {
@@ -1692,7 +1726,7 @@ do_file(const char *filename)
 	  error("couldn't convert 2 digits");
 	EnvInt hor_pos = (EnvInt) x;
 	current_env->hpos += hor_pos;
-	c = next_arg_begin();
+	c = next_arg_begin("jump-and-move (character)");
 	if ((int) c == '\n' || (int) c == EOF)
 	  error("character argument expected");
 	else
@@ -1703,10 +1737,8 @@ do_file(const char *filename)
       {
 	if (npages <= 0)
 	  fatal_command(command);
-	Char c = next_arg_begin();
-	if (c == '\n' || c == EOF)
-	  error("missing argument to 'c' command");
-	else
+	Char c = next_arg_begin("c");
+	if (c != '\n' && c != EOF)
 	  pr->set_ascii_char((unsigned char) c, current_env);
 	break;
       }
@@ -1714,7 +1746,7 @@ do_file(const char *filename)
       {
 	if (npages <= 0)
 	  fatal_command(command);
-	char *str_arg = get_string_arg();
+	char *str_arg = get_string_arg("C");
 	pr->set_special_char(str_arg, current_env);
 	a_delete str_arg;
 	break;
@@ -1725,7 +1757,7 @@ do_file(const char *filename)
       parse_D_command();
       break;
     case 'f':			// f: set font to number
-      current_env->fontno = get_integer_arg();
+      current_env->fontno = get_integer_arg("f");
       break;
     case 'F':			// F: obsolete, replaced by 'x F'
       {
@@ -1735,13 +1767,13 @@ do_file(const char *filename)
 	break;
       }
     case 'h':			// h: relative horizontal move
-      current_env->hpos += (EnvInt) get_integer_arg();
+      current_env->hpos += (EnvInt) get_integer_arg("h");
       break;
     case 'H':			// H: absolute horizontal positioning
-      current_env->hpos = (EnvInt) get_integer_arg();
+      current_env->hpos = (EnvInt) get_integer_arg("H");
       break;
     case 'm':			// m: glyph color
-      parse_color_command(current_env->col);
+      parse_color_command(current_env->col, "m");
       pr->change_color(current_env);
       break;
     case 'n':			// n: print end of line
@@ -1749,23 +1781,23 @@ do_file(const char *filename)
       if (npages <= 0)
 	fatal_command(command);
       pr->end_of_line();
-      (void) get_integer_arg();
-      (void) get_integer_arg();
+      (void) get_integer_arg("n (first ignored)");
+      (void) get_integer_arg("n (second ignored)");
       break;
     case 'N':			// N: print char with given int code
       if (npages <= 0)
 	fatal_command(command);
-      pr->set_numbered_char(get_integer_arg(), current_env);
+      pr->set_numbered_char(get_integer_arg("N"), current_env);
       break;
     case 'p':			// p: start new page with given number
       if (npages > 0)
 	pr->end_page(current_env->vpos);
       npages++;			// increment # of processed pages
-      pr->begin_page(get_integer_arg());
+      pr->begin_page(get_integer_arg("p"));
       current_env->vpos = 0;
       break;
     case 's':			// s: set point size
-      current_env->size = get_integer_arg();
+      current_env->size = get_integer_arg("s");
       if (current_env->height == current_env->size)
 	current_env->height = 0;
       break;
@@ -1774,7 +1806,7 @@ do_file(const char *filename)
 	char c;
 	if (npages <= 0)
 	  fatal_command(command);
-	char *str_arg = get_string_arg();
+	char *str_arg = get_string_arg("t");
 	size_t i = 0;
 	while ((c = str_arg[i++]) != '\0') {
 	  EnvInt w;
@@ -1789,8 +1821,8 @@ do_file(const char *filename)
 	char c;
 	if (npages <= 0)
 	  fatal_command(command);
-	EnvInt kern = (EnvInt) get_integer_arg();
-	char *str_arg = get_string_arg();
+	EnvInt kern = (EnvInt) get_integer_arg("u");
+	char *str_arg = get_string_arg("u");
 	size_t i = 0;
 	while ((c = str_arg[i++]) != '\0') {
 	  EnvInt w;
@@ -1801,10 +1833,10 @@ do_file(const char *filename)
 	break;
       }
     case 'v':			// v: relative vertical move
-      current_env->vpos += (EnvInt) get_integer_arg();
+      current_env->vpos += (EnvInt) get_integer_arg("v");
       break;
     case 'V':			// V: absolute vertical positioning
-      current_env->vpos = (EnvInt) get_integer_arg();
+      current_env->vpos = (EnvInt) get_integer_arg("V");
       break;
     case 'w':			// w: inform about paddable space
       break;
diff --git a/src/libs/libgroff/errarg.cpp b/src/libs/libgroff/errarg.cpp
index 593e2a57..6cb5fd12 100644
--- a/src/libs/libgroff/errarg.cpp
+++ b/src/libs/libgroff/errarg.cpp
@@ -121,7 +121,7 @@ void errprint(const char *format,
 	arg3.print();
 	break;
       default:
-	assert(0);
+	assert(0 == "unsupported format specifier given to errprint()");
       }
     }
     else