diff --git a/src/core/commands.c b/src/core/commands.c
index b2151c1e..06c2add6 100644
--- a/src/core/commands.c
+++ b/src/core/commands.c
@@ -129,9 +129,6 @@ COMMAND_REC *command_find(const char *cmd)
 	return NULL;
 }
 
-#define iscmdtype(c) \
-        ((c) == '-' || (c) == '+' || (c) == '@')
-
 static GSList *optlist_find(GSList *optlist, const char *option)
 {
 	while (optlist != NULL) {
@@ -240,21 +237,41 @@ static char *cmd_get_quoted_param(char **data)
 	return pos;
 }
 
-static int option_find(char **array, const char *item)
+/* Find specified option from list of options - the `option' might be
+   shortened version of the full command. Returns index where the
+   option was found, -1 if not found or -2 if there was multiple matches. */
+static int option_find(char **array, const char *option)
 {
 	char **tmp;
-	int index;
+	int index, found, len;
 
-	g_return_val_if_fail(array != NULL, 0);
-	g_return_val_if_fail(item != NULL, 0);
+	g_return_val_if_fail(array != NULL, -1);
+	g_return_val_if_fail(option != NULL, -1);
 
-	index = 0;
+	len = strlen(option);
+	g_return_val_if_fail(len > 0, -1);
+
+	found = -1; index = 0;
 	for (tmp = array; *tmp != NULL; tmp++, index++) {
-		if (g_strcasecmp(*tmp + iscmdtype(**tmp), item) == 0)
-			return index;
+		const char *text = *tmp + iscmdtype(**tmp);
+
+		if (g_strncasecmp(text, option, len) == 0) {
+			if (text[len] == '\0') {
+				/* full match */
+				return index;
+			}
+
+			if (found != -1) {
+				/* multiple matches - abort */
+				return -2;
+			}
+
+			/* partial match, check that it's the only one */
+			found = index;
+		}
 	}
 
-	return -1;
+	return found;
 }
 
 static int get_cmd_options(char **data, int ignore_unknown,
@@ -295,7 +312,12 @@ static int get_cmd_options(char **data, int ignore_unknown,
                                 *data = option;
 				return CMDERR_OPTION_UNKNOWN;
 			}
-			if (pos != -1) {
+			if (pos == -2 && !ignore_unknown) {
+                                /* multiple matches */
+				*data = option;
+				return CMDERR_OPTION_AMBIGUOUS;
+			}
+			if (pos >= 0) {
 				/* if we used a shortcut of parameter, put
 				   the whole parameter name in options table */
 				option = optlist[pos] + iscmdtype(*optlist[pos]);
diff --git a/src/core/commands.h b/src/core/commands.h
index 1f1dc8dd..fa553518 100644
--- a/src/core/commands.h
+++ b/src/core/commands.h
@@ -10,7 +10,8 @@ typedef struct {
 } COMMAND_REC;
 
 enum {
-	CMDERR_OPTION_UNKNOWN = -2, /* unknown -option */
+	CMDERR_OPTION_UNKNOWN = -3, /* unknown -option */
+	CMDERR_OPTION_AMBIGUOUS = -2, /* ambiguous -option */
 	CMDERR_OPTION_ARG_MISSING = -1, /* argument missing for -option */
 
         CMDERR_ERRNO, /* get the error from errno */
@@ -22,15 +23,20 @@ enum {
 	CMDERR_NOT_GOOD_IDEA /* not good idea to do, -yes overrides this */
 };
 
+/* Return the full command for `alias' */
 #define alias_find(alias) \
 	iconfig_get_str("aliases", alias, NULL)
 
-#define cmd_return_error(a) { signal_emit("error command", 1, GINT_TO_POINTER(a)); signal_stop(); return; }
-#define cmd_param_error(a) { cmd_params_free(free_arg); cmd_return_error(a); }
+/* Returning from command function with error */
+#define cmd_return_error(a) \
+	{ signal_emit("error command", 1, GINT_TO_POINTER(a)); signal_stop(); return; }
+#define cmd_param_error(a) \
+	{ cmd_params_free(free_arg); cmd_return_error(a); }
 
 extern GSList *commands;
-extern char *current_command;
+extern char *current_command; /* the command we're right now. */
 
+/* Bind command to specified function. */
 void command_bind_to(int pos, const char *cmd, const char *category, SIGNAL_FUNC func);
 #define command_bind(a, b, c) command_bind_to(1, a, b, c)
 #define command_bind_first(a, b, c) command_bind_to(0, a, b, c)
@@ -57,6 +63,8 @@ COMMAND_REC *command_find(const char *cmd);
    You can call this command multiple times for same command, options
    will be merged. If there's any conflicts with option types, the last
    call will override the previous */
+#define iscmdtype(c) \
+        ((c) == '-' || (c) == '+' || (c) == '@')
 void command_set_options(const char *cmd, const char *options);
 
 /* count can have these flags: */
diff --git a/src/fe-common/core/completion.c b/src/fe-common/core/completion.c
index 714d7934..6ed04964 100644
--- a/src/fe-common/core/completion.c
+++ b/src/fe-common/core/completion.c
@@ -173,6 +173,8 @@ GList *list_add_file(GList *list, const char *name)
 	struct stat statbuf;
 	char *fname;
 
+	g_return_val_if_fail(name != NULL, NULL);
+
 	fname = convert_home(name);
 	if (stat(fname, &statbuf) == 0) {
 		list = g_list_append(list, !S_ISDIR(statbuf.st_mode) ? g_strdup(name) :
@@ -191,6 +193,8 @@ GList *filename_complete(const char *path)
 	char *realpath, *dir, *basename, *name;
 	int len;
 
+	g_return_val_if_fail(path != NULL, NULL);
+
 	list = NULL;
 
 	/* get directory part of the path - expand ~/ */
@@ -237,6 +241,8 @@ static int is_base_command(const char *command)
 	GSList *tmp;
 	int len;
 
+	g_return_val_if_fail(command != NULL, FALSE);
+
 	/* find "command "s */
         len = strlen(command);
 	for (tmp = commands; tmp != NULL; tmp = tmp->next) {
@@ -255,6 +261,8 @@ static GList *completion_get_settings(const char *key)
 	GSList *tmp, *sets;
 	int len;
 
+	g_return_val_if_fail(key != NULL, NULL);
+
 	sets = settings_get_sorted();
 
 	len = strlen(key);
@@ -275,6 +283,8 @@ static GList *completion_get_bool_settings(const char *key)
 	GSList *tmp, *sets;
 	int len;
 
+	g_return_val_if_fail(key != NULL, NULL);
+
 	sets = settings_get_sorted();
 
 	len = strlen(key);
@@ -297,6 +307,8 @@ static GList *completion_get_commands(const char *cmd, char cmdchar)
 	char *word;
 	int len;
 
+	g_return_val_if_fail(cmd != NULL, NULL);
+
 	len = strlen(cmd);
 	complist = NULL;
 	for (tmp = commands; tmp != NULL; tmp = tmp->next) {
@@ -323,6 +335,8 @@ static GList *completion_get_subcommands(const char *cmd)
 	char *spacepos;
 	int len, skip;
 
+	g_return_val_if_fail(cmd != NULL, NULL);
+
 	/* get the number of chars to skip at the start of command. */
 	spacepos = strrchr(cmd, ' ');
 	skip = spacepos == NULL ? 0 :
@@ -345,12 +359,38 @@ static GList *completion_get_subcommands(const char *cmd)
 	return complist;
 }
 
+GList *completion_get_options(const char *cmd, const char *option)
+{
+	COMMAND_REC *rec;
+	GList *list;
+	char **tmp;
+	int len;
+
+	g_return_val_if_fail(cmd != NULL, NULL);
+	g_return_val_if_fail(option != NULL, NULL);
+
+	rec = command_find(cmd);
+	if (rec == NULL) return NULL;
+
+	list = NULL;
+	len = strlen(option);
+	for (tmp = rec->options; *tmp != NULL; tmp++) {
+		if (len == 0 || g_strncasecmp(*tmp, option, len) == 0)
+                        list = g_list_append(list, g_strconcat("-", *tmp + iscmdtype(**tmp), NULL));
+	}
+
+	return list;
+}
+
 /* split the line to command and arguments */
 static char *line_get_command(const char *line, char **args, int aliases)
 {
 	const char *ptr, *cmdargs;
 	char *cmd, *checkcmd;
 
+	g_return_val_if_fail(line != NULL, NULL);
+	g_return_val_if_fail(args != NULL, NULL);
+
 	cmd = checkcmd = NULL; *args = "";
 	cmdargs = NULL; ptr = line;
 
@@ -391,6 +431,8 @@ static char *expand_aliases(const char *line)
 {
         char *cmd, *args, *ret;
 
+	g_return_val_if_fail(line != NULL, NULL);
+
 	cmd = line_get_command(line, &args, TRUE);
 	if (cmd == NULL) return g_strdup(line);
 	if (*args == '\0') return cmd;
@@ -448,16 +490,27 @@ static void sig_complete_word(GList **list, WINDOW_REC *window,
 		return;
 	}
 
-	/* complete parameters */
 	cmd = line_get_command(line, &args, FALSE);
-	if (cmd != NULL) {
-		signal = g_strconcat("complete command ", cmd, NULL);
-		signal_emit(signal, 5, list, window, word, args, want_space);
-
-		g_free(signal);
-		g_free(cmd);
+	if (cmd == NULL) {
+		g_free(line);
+		return;
 	}
 
+	/* we're completing -option? */
+	if (*word == '-') {
+                *list = completion_get_options(cmd, word+1);
+		g_free(cmd);
+		g_free(line);
+		return;
+	}
+
+	/* complete parameters */
+	signal = g_strconcat("complete command ", cmd, NULL);
+	signal_emit(signal, 5, list, window, word, args, want_space);
+
+	g_free(signal);
+	g_free(cmd);
+
 	g_free(line);
 }
 
diff --git a/src/fe-common/core/fe-core-commands.c b/src/fe-common/core/fe-core-commands.c
index 3b725bae..894eae6f 100644
--- a/src/fe-common/core/fe-core-commands.c
+++ b/src/fe-common/core/fe-core-commands.c
@@ -314,10 +314,13 @@ static void event_cmderror(gpointer errorp, const char *arg)
 		printtext(NULL, NULL, MSGLEVEL_CLIENTERROR, g_strerror(errno));
 		break;
 	case CMDERR_OPTION_UNKNOWN:
-		printtext(NULL, NULL, MSGLEVEL_CLIENTERROR, "Unknown argument: %s", arg);
+		printformat(NULL, NULL, MSGLEVEL_CLIENTERROR, IRCTXT_OPTION_UNKNOWN, arg);
+		break;
+	case CMDERR_OPTION_AMBIGUOUS:
+		printformat(NULL, NULL, MSGLEVEL_CLIENTERROR, IRCTXT_OPTION_AMBIGUOUS, arg);
 		break;
 	case CMDERR_OPTION_ARG_MISSING:
-		printtext(NULL, NULL, MSGLEVEL_CLIENTERROR, "Missing required argument for: %s", arg);
+		printformat(NULL, NULL, MSGLEVEL_CLIENTERROR, IRCTXT_OPTION_MISSING_ARG, arg);
 		break;
 	default:
 		printtext(NULL, NULL, MSGLEVEL_CLIENTERROR, ret_texts[error]);
diff --git a/src/fe-common/core/module-formats.c b/src/fe-common/core/module-formats.c
index a141d273..6f704e99 100644
--- a/src/fe-common/core/module-formats.c
+++ b/src/fe-common/core/module-formats.c
@@ -91,6 +91,9 @@ FORMAT_REC fecommon_core_formats[] = {
 
 	{ "not_toggle", "Value must be either ON, OFF or TOGGLE", 0 },
 	{ "perl_error", "Perl error: $0", 1, { 0 } },
+	{ "option_unknown", "Unknown option: $0", 1, { 0 } },
+	{ "option_ambiguous", "Ambiguous option: $0", 1, { 0 } },
+	{ "option_missing_arg", "Missing required argument for: $0", 1, { 0 } },
 
 	{ NULL, NULL, 0 }
 };
diff --git a/src/fe-common/core/module-formats.h b/src/fe-common/core/module-formats.h
index cc38d4ae..9c5b1f15 100644
--- a/src/fe-common/core/module-formats.h
+++ b/src/fe-common/core/module-formats.h
@@ -63,7 +63,10 @@ enum {
 	IRCTXT_FILL_6,
 
 	IRCTXT_NOT_TOGGLE,
-	IRCTXT_PERL_ERROR
+	IRCTXT_PERL_ERROR,
+	IRCTXT_OPTION_UNKNOWN,
+	IRCTXT_OPTION_AMBIGUOUS,
+	IRCTXT_OPTION_MISSING_ARG
 };
 
 extern FORMAT_REC fecommon_core_formats[];