diff --git a/autoload/easy_align.vim b/autoload/easy_align.vim
index c0a5a66..0a618ad 100644
--- a/autoload/easy_align.vim
+++ b/autoload/easy_align.vim
@@ -143,7 +143,9 @@ function! s:echon(l, n, r, d, o, warn)
   \ [['Identifier', a:d == ' ' ? '\ ' : (a:d == '\' ? '\\' : a:d)]])
   if a:r == -1 | call add(tokens, ['Comment', ')']) | endif
   call add(tokens, ['Statement', empty(a:o) ? '' : ' '.string(a:o)])
-  call add(tokens, ['WarningMsg', a:warn])
+  if !empty(a:warn)
+    call add(tokens, ['WarningMsg', ' ('.a:warn.')'])
+  endif
 
   call s:echon_(tokens)
 endfunction
@@ -561,7 +563,7 @@ function! s:atoi(str)
   return (a:str =~ '^[0-9]\+$') ? str2nr(a:str) : a:str
 endfunction
 
-function! s:interactive(modes, vis, opts)
+function! s:interactive(modes, vis, opts, delims)
   let mode = s:shift(a:modes, 1)
   let n    = ''
   let ch   = ''
@@ -607,9 +609,21 @@ function! s:interactive(modes, vis, opts)
     elseif ch == "\<C-I>"
       let opts['idt'] = s:shift(vals['indentation'], 1)
     elseif ch == "\<C-L>"
-      let opts['lm'] = s:atoi(s:input("Left margin: ", get(opts, 'lm', ''), a:vis))
+      let lm = s:input("Left margin: ", get(opts, 'lm', ''), a:vis)
+      if empty(lm)
+        let warn = 'Set to default. Input 0 to remove it'
+        silent! call remove(opts, 'lm')
+      else
+        let opts['lm'] = s:atoi(lm)
+      endif
     elseif ch == "\<C-R>"
-      let opts['rm'] = s:atoi(s:input("Right margin: ", get(opts, 'rm', ''), a:vis))
+      let rm = s:input("Right margin: ", get(opts, 'rm', ''), a:vis)
+      if empty(rm)
+        let warn = 'Set to default. Input 0 to remove it'
+        silent! call remove(opts, 'rm')
+      else
+        let opts['rm'] = s:atoi(rm)
+      endif
     elseif ch == "\<C-U>"
       let opts['iu'] = s:shift(vals['ignore_unmatched'], 1)
     elseif ch == "\<C-G>"
@@ -636,24 +650,40 @@ function! s:interactive(modes, vis, opts)
     elseif ch == "\<C-_>" || ch == "\<C-X>"
       let prompt = 'Regular expression: '
       let ch = s:input(prompt, '', a:vis)
-      if !empty(ch)
+      let s:prev_echon_len = len(prompt . ch)
+      if !empty(ch) && s:valid_regexp(ch)
         let regx = 1
-        let s:prev_echon_len = len(prompt . ch)
         break
+      else
+        let warn = 'Invalid regular expression: '.ch
       endif
     elseif ch =~ '[[:print:]]'
-      break
+      if has_key(a:delims, ch)
+        break
+      else
+        let warn = 'Unknown delimiter key: '.ch
+      endif
     else
-      let warn = ' - Invalid character'
+      let warn = 'Invalid character'
     endif
   endwhile
   return [mode, n, ch, s:normalize_options(opts), regx]
 endfunction
 
-function! s:test_regexp(regexp)
-  try   | call matchlist('', a:regexp)
-  catch | call s:exit("Invalid regular expression: ". a:regexp)
+function! s:valid_regexp(regexp)
+  try
+    call matchlist('', a:regexp)
+  catch
+    return 0
   endtry
+  return 1
+endfunction
+
+function! s:test_regexp(regexp)
+  if !s:valid_regexp(a:regexp)
+    call s:exit('Invalid regular expression: '. a:regexp)
+  endif
+  return a:regexp
 endfunction
 
 function! s:parse_args(args)
@@ -700,7 +730,7 @@ function! s:parse_args(args)
 
   " Found regexp
   if !empty(matches)
-    return [matches[1], matches[2], opts, 1]
+    return [matches[1], s:test_regexp(matches[2]), opts, 1]
   else
     let tokens = matchlist(args, '^\([1-9][0-9]*\|-[0-9]*\|\*\*\?\)\?\s*\(.\{-}\)\?$')
     return [tokens[1], tokens[2], opts, 0]
@@ -735,12 +765,17 @@ function! s:align(bang, first_line, last_line, expr)
   " Heuristically determine if the user was in visual mode
   let vis    = a:first_line == line("'<") && a:last_line == line("'>")
 
+  let delimiters = s:easy_align_delimiters_default
+  if exists('g:easy_align_delimiters')
+    let delimiters = extend(copy(delimiters), g:easy_align_delimiters)
+  endif
+
   if empty(a:expr)
-    let [mode, n, ch, opts, regexp] = s:interactive(copy(modes), vis, opts)
+    let [mode, n, ch, opts, regexp] = s:interactive(copy(modes), vis, opts, delimiters)
   else
     let [n, ch, opts, regexp] = s:parse_args(a:expr)
     if empty(n) && empty(ch)
-      let [mode, n, ch, opts, regexp] = s:interactive(copy(modes), vis, opts)
+      let [mode, n, ch, opts, regexp] = s:interactive(copy(modes), vis, opts, delimiters)
     elseif empty(ch)
       " Try swapping n and ch
       let [n, ch] = ['', n]
@@ -757,13 +792,7 @@ function! s:align(bang, first_line, last_line, expr)
     let nth = n
   endif
 
-  let delimiters = s:easy_align_delimiters_default
-  if exists('g:easy_align_delimiters')
-    let delimiters = extend(copy(delimiters), g:easy_align_delimiters)
-  endif
-
   if regexp
-    call s:test_regexp(ch)
     let dict = { 'pattern': ch }
   else
     " Resolving command-line ambiguity
diff --git a/test/basic.script b/test/basic.script
index 946899c..3057f2d 100644
--- a/test/basic.script
+++ b/test/basic.script
@@ -1 +1 @@
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349Gpvip:EasyAlign*/|/{'ml':'~', 'mrr': 4}
362G:let g:easy_align_delimiters = { 'd': { 'pattern': '\s\+\(\S\+\s*[;=]\)\@=', 'left_margin': 0, 'right_margin': 0 } }
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Pvip:EasyAlign*/-\+/{'da': L}
Pvip:EasyAlign/-\+/{'da': c}
Pvip:EasyAlign*/-\+/{'delimiter_align':'C'}
Pvip:EasyAlign*/-\+/{'da': 'x'}
381Gpvip:EasyAlign/-\+/{'da':r}
:let g:easy_align_delimiter_align = 'l'
Pvip:EasyAlign/-\+/
Pvip:EasyAlign*/-\+/
:unlet g:easy_align_delimiter_align
:let g:easy_align_delimiters['\'] = { 'pattern': '-\+', 'delimiter_align': 'c' }
Pvip
\Pvip
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*\Pvip:EasyAlign    *\\   {'da':l}
Pvip:EasyAlign*\\
Pvip:EasyAlign*\\{'da': 'R'}
377GvipjyPvip:EasyAlign\ {'l': '@@@'}
gv:EasyAlign     2          \          {'l': '{{{'}
507Gvipjygv:EasyAlign=
Pvip:EasyAlign =  {'idt': s}
Pvip:EasyAlign= {'idt': d}
Pvip:EasyAlign**={'indentation': 'd'}
Pvip:EasyAlign!=
Pvip:EasyAlign! **= {'indent': s}
Pvip:EasyAlign!* = {'idt': D}
Pvip:EasyAlign! ={'idt':'S'}
507GPvip:EasyAlign-={'idt':d}
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507GPljjjj$:EasyAlign = {'idt': s}
Pljjjj$:EasyAlign={'indent':d}
Phhxxvip:EasyAlign={'idt':'s'}
525Gvipjy507GPPvip:EasyAlign*={'idt':s}
Pvip:EasyAlign!**={'idt':s}
Pvip:EasyAlign = {'idt': D}
525G^hhr1jr1jr1jr1jr1llkkkk$:EasyAlign = { 'idt': s }
513GvipjyPvip:EasyAlign*={'idt':n}
Pvip:EasyAlign = { 'idt': N }
Pvip:EasyAlign!*= {'idt': 'n'}
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903Gpvip:EasyAlign**|{'m':'llc'}
913Gpvip:s/^|//
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107GvipjyPvip
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4Gvipy4GP7Gojkkvip:EasyAlign /1/{'ml':'{{', 'mr-r':'}}'}
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349Gpvip:EasyAlign*/|/{'ml':'~', 'mrr': 4}
362G:let g:easy_align_delimiters = { 'd': { 'pattern': '\s\+\(\S\+\s*[;=]\)\@=', 'left_margin': 0, 'right_margin': 0 } }
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2 382Gvipjyvip:EasyAlign/-\+/
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Pvip:EasyAlign*/-\+/{'da': L}
Pvip:EasyAlign/-\+/{'da': c}
Pvip:EasyAlign*/-\+/{'delimiter_align':'C'}
Pvip:EasyAlign*/-\+/{'da': 'x'}
381Gpvip:EasyAlign/-\+/{'da':r}
:let g:easy_align_delimiter_align = 'l'
Pvip:EasyAlign/-\+/
Pvip:EasyAlign*/-\+/
:unlet g:easy_align_delimiter_align
:let g:easy_align_delimiters['\'] = { 'pattern': '-\+', 'delimiter_align': 'c' }
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*\Pvip:EasyAlign    *\\   {'da':l}
Pvip:EasyAlign*\\
Pvip:EasyAlign*\\{'da': 'R'}
377GvipjyPvip:EasyAlign\ {'l': '@@@'}
gv:EasyAlign     2          \          {'l': '{{{'}
507Gvipjygv:EasyAlign=
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Pvip:EasyAlign= {'idt': d}
Pvip:EasyAlign**={'indentation': 'd'}
Pvip:EasyAlign!=
Pvip:EasyAlign! **= {'indent': s}
Pvip:EasyAlign!* = {'idt': D}
Pvip:EasyAlign! ={'idt':'S'}
507GPvip:EasyAlign-={'idt':d}
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507GPljjjj$:EasyAlign = {'idt': s}
Pljjjj$:EasyAlign={'indent':d}
Phhxxvip:EasyAlign={'idt':'s'}
525Gvipjy507GPPvip:EasyAlign*={'idt':s}
Pvip:EasyAlign!**={'idt':s}
Pvip:EasyAlign = {'idt': D}
525G^hhr1jr1jr1jr1jr1llkkkk$:EasyAlign = { 'idt': s }
513GvipjyPvip:EasyAlign*={'idt':n}
Pvip:EasyAlign = { 'idt': N }
Pvip:EasyAlign!*= {'idt': 'n'}
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903Gpvip:EasyAlign**|{'m':'llc'}
913Gpvip:s/^|//
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			2=993Gvip


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3 Pvip:EasyAlign{'mode_seq':'lrc**'}
2 Pvip:EasyAlign{'ms':'lccr**'}
 
diff --git a/test/regexp.script b/test/regexp.script
index ca8b777..85508ee 100644
--- a/test/regexp.script
+++ b/test/regexp.script
@@ -1 +1 @@
-4Gvipjyvip:EasyAlign:
Pvip:EasyAlign*:
Pvip:EasyAlign-:
Pvip:EasyAlign * :
Pvip:EasyAlign -2 :
Pvip:EasyAlign -2:
Pvip:easyA€kb€kb€kb€kb€kbEasAli€kb€kb€kbyAlign *:
Pvip:EasyAlign;
Pvip:EasyAlign /;/
Pvip:EasyAlign/;/
Pvip:EasyAlign*/;/
Pvip:e€kbEasyAlign/[:;]\+/
Pvip:EasyAlign*/[:;]\+/
Pvip:EasyAlign* /[:;]\+/
Pvip:EasyAlign */[:;]\+/
Pvip:EasyAlign   *   [:€kb€kb/[:;]\+/   
Pvip:EasyAlign*[:;]\+€kb€kb€kb€kb€kb€kb€kb=/[€kb€kb€kb-/[:;]\+/
Pvip:EasyAlign-2/[:;\€kb\€kb]\+/
Pvip:EasyAlign/[:;]\+/{ 'l': '<<<', 'r': '>>>'}  
Pvip:EasyAlign/[:;]\+/{'l':''m€kb, 's': 1}
Pvip:EasyAlign * /€kb /[:;]€kb\€kb]\+/ {'stick_to': 1, 'le': '???', 'marr': '~~~'}  
Pvip:EasyAlign /../
Pvip:EasyAlign*/../
Pvip:EasyAlign ** €kb/[:;]/€kb€kb\+]/
Pvip:EasyAlign/[:;\€kb\€kb]\+/'€kb{'rm':'____'}
Pvip:EasyAlign**[€kb/[:;]\+/
Pvip:EasyAlign!**/[:;]\+/
Pfbjfm:EasyAlign/[:;]\+/
90Gvip:EasyAlign/#/{'is':['String'],'iu':0}
93Gpvip:EasyAlign*/\s*/{'l':'(', 'r': ')'}

+4Gvipjyvip:EasyAlign:
Pvip:EasyAlign*:
Pvip:EasyAlign-:
Pvip:EasyAlign * :
Pvip:EasyAlign -2 :
Pvip:EasyAlign -2:
Pvip:EasyAlign *:
Pvip:EasyAlign;
Pvip:EasyAlign /;/
Pvip:EasyAlign/;/
Pvip:EasyAlign*/;/
Pvip:EasyAlign/[:;]\+/
Pvip:EasyAlign*/[:;]\+/
Pvip:EasyAlign* /[:;]\+/
Pvip:EasyAlign */[:;]\+/
Pvip:EasyAlign   *   /[:;]\+/   
Pvip:EasyAlign-/[:;]\+/
Pvip:EasyAlign-2/[:;]\+/
Pvip:EasyAlign/[:;]\+/{ 'l': '<<<', 'r': '>>>'}  
Pvip:EasyAlign/[:;]\+/{'l':'', 's': 1}
Pvip:EasyAlign *  /[:;]\+/ {'stick_to': 1, 'le': '???', 'marr': '~~~'}  
Pvip:EasyAlign /../
Pvip:EasyAlign*/../
Pvip:EasyAlign **/[:;\+]/
Pvip:EasyAlign/[:;]\+/{'rm':'____'}
Pvip:EasyAlign**/[:;]\+/
Pvip:EasyAlign!**/[:;]\+/
Pfbjfm:EasyAlign/[:;]\+/
90Gvip:EasyAlign/#/{'is':['String'],'iu':0}
93Gpvip:EasyAlign*/\s*/{'l':'(', 'r': ')'}