diff --git a/Docs/src/defines.but b/Docs/src/defines.but
index a63b2f55..db48443e 100644
--- a/Docs/src/defines.but
+++ b/Docs/src/defines.but
@@ -30,7 +30,7 @@ If \e{/file} is used, the entire text file specified (including whitespace and n
 
 \S1{undef} !undef
 
-\c gflag
+\c [/noerrors] gflag [...]
 
 Removes an item from the global define list. Note that $\{SYMBOL\} where SYMBOL is undefined will be translated to "$\{SYMBOL\}".
 
diff --git a/Docs/src/history.but b/Docs/src/history.but
index 632e1ae6..c728fc25 100644
--- a/Docs/src/history.but
+++ b/Docs/src/history.but
@@ -24,6 +24,8 @@ Released on ??? ??th, 20??
 
 \b Fixed !macroundef of last defined macro bug
 
+\b !undef issues warnings instead of errors
+
 \b MakeNSIS prints -CMDHELP to stdout (\W{http://sf.net/p/nsis/bugs/1203}{bug #1203})
 
 \S2{} Translations
diff --git a/Source/build.h b/Source/build.h
index 42a5850b..d745c0c7 100644
--- a/Source/build.h
+++ b/Source/build.h
@@ -95,6 +95,7 @@ typedef enum {
   DW_PP_DELFILE_NOMATCH = DW_PP_DELFILE_DELERROR,
   DW_PP_VERBOSE_POP_EMPTY_STACK = 6150,
   //DW_PP_VERBOSE_BAD_LEVEL = 6151?, // 2.x failed to issue a warning. 3.x currently aborts with hard error.
+  DW_PP_UNDEF_UNDEFINED = 6155,
   DW_INCLUDE_NONFATAL_NOT_FOUND = 7000, // reserved ..7009
   DW_FILE_NONFATAL_NOT_FOUND = 7010, // reserved ..7019
   DW_LANGSTRING_OVERLONGLENGTH = 7020, // reserved ..7024
diff --git a/Source/scriptpp.cpp b/Source/scriptpp.cpp
index bc81c7a0..17513a8d 100644
--- a/Source/scriptpp.cpp
+++ b/Source/scriptpp.cpp
@@ -1010,12 +1010,26 @@ int CEXEBuild::pp_define(LineParser&line)
 
 int CEXEBuild::pp_undef(LineParser&line)
 {
-  if (definedlist.del(line.gettoken_str(1)))
+  UINT noerr = false, stopswitch = false, ti = 1, handled = 0;
+  for (; ti < line.getnumtokens(); ++ti)
   {
-    ERROR_MSG(_T("!undef: \"%") NPRIs _T("\" not defined!\n"), line.gettoken_str(1));
-    return PS_ERROR; // Should this be a warning?
+    const TCHAR *name = line.gettoken_str(ti);
+    if (!stopswitch && !_tcsicmp(name, _T("/noerrors")))
+    {
+      ++noerr;
+      continue;
+    }
+    stopswitch = ++handled;
+    if (definedlist.del(name) && !noerr)
+      warning_fl(DW_PP_UNDEF_UNDEFINED, _T("!undef: \"%") NPRIs _T("\" not defined!"), name);
+    else
+      SCRIPT_MSG(_T("!undef: \"%") NPRIs _T("\"\n"), name);
+  }
+  if (!handled)
+  {
+    PRINTHELP();
+    return PS_ERROR;
   }
-  SCRIPT_MSG(_T("!undef: \"%") NPRIs _T("\"\n"), line.gettoken_str(1));
   return PS_OK;
 }
 
diff --git a/Source/tokens.cpp b/Source/tokens.cpp
index c10491e3..1b1cb580 100644
--- a/Source/tokens.cpp
+++ b/Source/tokens.cpp
@@ -271,7 +271,7 @@ static tokenType tokenlist[TOK__LAST] =
 {TOK_P_IFNDEF,_T("!ifndef"),1,-1,_T("symbol [| symbol2 [& symbol3 [...]]]"),TP_ALL},
 {TOK_P_ENDIF,_T("!endif"),0,0,_T(""),TP_ALL},
 {TOK_P_DEFINE,_T("!define"),1,5,_T("[/ifndef | /redef] ([/date|/utcdate] symbol [value]) | (/file symbol filename) | (/math symbol val1 OP val2)\n    OP=(+ - * / % << >> >>> & | ^ ~ ! && ||)"),TP_ALL},
-{TOK_P_UNDEF,_T("!undef"),1,0,_T("symbol"),TP_ALL},
+{TOK_P_UNDEF,_T("!undef"),1,-1,_T("[/noerrors] symbol"),TP_ALL},
 {TOK_P_ELSE,_T("!else"),0,-1,_T("[if[macro][n][def] ...]"),TP_ALL},
 {TOK_P_ECHO,_T("!echo"),1,0,_T("message"),TP_ALL},
 {TOK_P_WARNING,_T("!warning"),0,1,_T("[warning_message]"),TP_ALL},