Index: global.c
===================================================================
--- global.c	(revision 5095)
+++ global.c	(working copy)
@@ -544,6 +544,7 @@
 	N_("Copy the current line and store it in the cutbuffer");
     const char *nano_indent_msg = N_("Indent the current line");
     const char *nano_unindent_msg = N_("Unindent the current line");
+    const char *nano_whitespace_to_tabs_msg = N_("Convert leading whitespace to tabs");
     const char *nano_undo_msg = N_("Undo the last operation");
     const char *nano_redo_msg = N_("Redo the last undone operation");
 #endif
@@ -799,7 +800,9 @@
     add_to_funcs(do_indent_void, MMAIN,
 	N_("Indent Text"), IFSCHELP(nano_indent_msg), TOGETHER, NOVIEW);
     add_to_funcs(do_unindent, MMAIN,
-	N_("Unindent Text"), IFSCHELP(nano_unindent_msg), BLANKAFTER, NOVIEW);
+	N_("Unindent Text"), IFSCHELP(nano_unindent_msg), TOGETHER, NOVIEW);
+    add_to_funcs(do_whitespace_to_tabs, MMAIN,
+	N_("Convert leading whitespace to tabs"), IFSCHELP(nano_whitespace_to_tabs_msg), BLANKAFTER, NOVIEW);
 
     add_to_funcs(do_undo, MMAIN,
 	N_("Undo"), IFSCHELP(nano_undo_msg), TOGETHER, NOVIEW);
@@ -1035,6 +1038,7 @@
     add_to_sclist(MMAIN, "M-6", do_copy_text, 0);
     add_to_sclist(MMAIN, "M-}", do_indent_void, 0);
     add_to_sclist(MMAIN, "M-{", do_unindent, 0);
+    add_to_sclist(MMAIN, "M-1", do_whitespace_to_tabs, 0);
     add_to_sclist(MMAIN, "M-U", do_undo, 0);
     add_to_sclist(MMAIN, "M-E", do_redo, 0);
 #endif
Index: proto.h
===================================================================
--- proto.h	(revision 5095)
+++ proto.h	(working copy)
@@ -641,6 +641,7 @@
 #ifndef NANO_TINY
 void do_indent(ssize_t cols);
 void do_indent_void(void);
+void do_whitespace_to_tabs(void);
 void do_unindent(void);
 void do_undo(void);
 void do_redo(void);
Index: text.c
===================================================================
--- text.c	(revision 5095)
+++ text.c	(working copy)
@@ -370,6 +370,84 @@
     do_indent(-tabsize);
 }
 
+/* Convert leading whitespace to tabs on the current line or all
+ * lines covered by the mark if the mark is on. */
+void do_whitespace_to_tabs(void)
+{
+    filestruct *top, *bot, *f;
+    size_t top_x, bot_x, line_len, i, diff_len_ws,
+        spaces, tabs, tabs_needed, ws_len, new_len;
+
+    assert(openfile->current != NULL && openfile->current->data != NULL);
+
+    /* If tabsize is zero, get out. */
+    if (tabsize == 0)
+        return;
+
+    /* If the mark is on, use all lines covered by the mark. */
+    if (openfile->mark_set) {
+        mark_order((const filestruct **)&top, &top_x,
+          (const filestruct **)&bot, &bot_x, NULL);
+        /* Otherwise, use the current line. */
+    } else {
+        top = openfile->current;
+        bot = top;
+    }
+
+    /* Go through each line of the text. */
+    for (f = top; f != bot->next; f = f->next) {
+
+        line_len = strlen(f->data);
+        spaces = 0;
+        tabs = 0;
+
+        /* Calculate how much space the whitespace is using. */
+        for (i = 0; i < line_len; i++) {
+            if (f->data[i] == ' ') {
+                spaces++;
+            } else if (f->data[i] == '\t') {
+                tabs++;
+            } else {
+                break;
+            }
+        }
+
+        /* If there's no leading spaces there's nothing to do. */
+        if (spaces == 0)
+            continue;
+
+        ws_len = spaces + tabs;
+
+        /* Round up to closest tab width. */
+        tabs_needed = ((spaces + tabsize - 1) / tabsize) + tabs;
+
+        new_len = line_len - ws_len + tabs_needed;
+        /* Fill up the first part with tabs. */
+        charset(f->data, '\t', tabs_needed);
+        if (tabs_needed < ws_len) {
+            /* Move the line data to it's new position. */
+            charmove(f->data + tabs_needed, f->data + ws_len, line_len - ws_len + 1);
+        }
+
+        openfile->totsize -= line_len - new_len;
+
+        /* Adjust the cursor position. */
+        if (openfile->mark_set && f == openfile->mark_begin &&
+            openfile->mark_begin_x >= ws_len)
+            openfile->mark_begin_x -= line_len - new_len + (spaces / tabsize);
+
+        diff_len_ws = ws_len - tabs_needed;
+        if (openfile->current_x > 0 && openfile->current_x > diff_len_ws)
+            openfile->current_x -= diff_len_ws;
+
+        /* Mark the file as modified. */
+        set_modified();
+
+        /* Update the screen. */
+        edit_refresh_needed = TRUE;
+    }
+}
+
 #define redo_paste undo_cut
 #define undo_paste redo_cut