diff --git a/Docs/src/defines.but b/Docs/src/defines.but
index 747d3bbe..b16d989d 100644
--- a/Docs/src/defines.but
+++ b/Docs/src/defines.but
@@ -10,15 +10,19 @@ Define/conditional compilation related commands:
 
 \S1{define} !define
 
-\c [/date] gflag [value]
+\c ([/date] gflag [value]) | (/math gflag val1 OP val2)
 
-This command will add 'gflag' to the global define list. This will have a similar effect as using the /D switch on the command line (only the define only becomes effective after the !define command).
+This command will add \e{gflag} to the global define list. This will have a similar effect as using the /D switch on the command line (only the define only becomes effective after the !define command).
 
 If \e{/date} is used, \e{value} will be passed into strftime and the result will be used as the value of \e{gflag}. strftime converts special symbols into certain parts of the current time or date. For example, %H will be converted into the current hour in 24-hour format. For a complete list of available symbols, search for strftime on \W{http://msdn.microsoft.com/}{MSDN}. On POSIX, you can get the list by using \c{man strftime}.
 
+If \e{/math} is used, the result of 'val1 OP val2', where OP may be +,-,*,/ or % , will be used as the value of \e{gflag}. Note that val1 AND val2 MUST be integer values!
+
 \c !define USE_SOMETHING
 \c !define VERSION 1.2
 \c !define /date NOW "%H:%M:%S %d %b, %Y"
+\c !define /math RESULT 3 + 10
+\c !define /math REST 15 % ${RESULT}
 
 \S1{undef} !undef
 
diff --git a/Source/Tests/preprocessor.nsi b/Source/Tests/preprocessor.nsi
index d1fb0349..1446143a 100644
--- a/Source/Tests/preprocessor.nsi
+++ b/Source/Tests/preprocessor.nsi
@@ -84,6 +84,46 @@ f
  !error "!if 'test' == 'test' is true!"
 !endif
 
+; testing of two math functions and a macro hack :)
+!define increase "!insertmacro increase"
+!macro increase DEFINE
+  !define /math ${DEFINE}_MACROTEMP ${${DEFINE}} + 1
+  !undef ${DEFINE}
+  !define ${DEFINE} ${${DEFINE}_MACROTEMP}
+  !undef ${DEFINE}_MACROTEMP
+!macroend
+
+!define number1 1 #  1
+!define /math number2 2 + 3
+!define /math number3 ${number2} - ${number1}
+${increase} number3
+!define /math number4 2 * ${number3}
+!define /math number5 ${number4} % 3
+
+!if ${number1} != 1
+  !error "number1 != 1"
+!endif
+
+!if ${number2} != 5
+  !error "number1 != 5"
+!endif
+
+!if ${number3} != 5
+  !error "number1 != 5"
+!endif
+
+!if ${number4} != 10
+  !error "number1 != 10"
+!endif
+
+!if ${number5} != 1
+  !error "number1 != 1"
+!endif
+
+!undef number1
+!undef number2
+!undef number3
+; end math functions
 
 # this should just give a warning, not an error
 !include /NONFATAL file_that_doesnt_exist.nsh
diff --git a/Source/script.cpp b/Source/script.cpp
index a94343f2..385d23c2 100644
--- a/Source/script.cpp
+++ b/Source/script.cpp
@@ -405,7 +405,7 @@ parse_again:
     int istrue=0;
 
     int mod=0;
-	  
+  
     int p=0;
     
     if (tkid == TOK_P_IF) {
@@ -2698,7 +2698,7 @@ int CEXEBuild::doCommand(int which_token, LineParser &line)
         value=line.gettoken_str(3);
 
         time_t rawtime;
-		    time(&rawtime);
+        time(&rawtime);
 
         datebuf[0]=0;
         size_t s=strftime(datebuf,sizeof(datebuf),value,localtime(&rawtime));
@@ -2711,6 +2711,40 @@ int CEXEBuild::doCommand(int which_token, LineParser &line)
         value=datebuf;
 
         date=true;
+
+      } else if (!stricmp(define,"/math")) {
+      
+        int value1;
+        int value2;
+        char *mathop;
+        
+        if (line.getnumtokens()!=6) PRINTHELP()
+
+        define = line.gettoken_str(2);
+        value1 = line.gettoken_int(3));
+        mathop = line.gettoken_str(4);
+        value2 = line.gettoken_int(5);
+
+        if (!strcmp(mathop,"+")) {
+          sprintf(value,"%d",value1+value2);
+        } else if (!strcmp(mathop,"-")) {
+          sprintf(value,"%d",value1-value2);
+        } else if (!strcmp(mathop,"*")) {
+          sprintf(value,"%d",value1*value2);
+        } else if (!strcmp(mathop,"%")) {
+          if (value2==0) {
+            ERROR_MSG("!define /math: division by zero! (\"%i / %i\")\n",value1,value2);
+            return PS_ERROR;
+          }
+          sprintf(value,"%d",value1/value2);
+        } else if (!strcmp(mathop,"%")) {
+          if (value2==0) {
+            ERROR_MSG("!define /math: division by zero! (\"%i %% %i\")\n",value1,value2);
+            return PS_ERROR;
+          }
+          sprintf(value,"%d",value1%value2);
+        } else PRINTHELP()
+
       } else {
         if (line.getnumtokens()==4) PRINTHELP()
 
diff --git a/Source/tokens.cpp b/Source/tokens.cpp
index d9805ce3..7bdae21e 100644
--- a/Source/tokens.cpp
+++ b/Source/tokens.cpp
@@ -229,7 +229,7 @@ static tokenType tokenlist[TOK__LAST] =
 {TOK_P_IFDEF,"!ifdef",1,-1,"symbol [| symbol2 [& symbol3 [...]]]",TP_ALL},
 {TOK_P_IFNDEF,"!ifndef",1,-1,"symbol [| symbol2 [& symbol3 [...]]]",TP_ALL},
 {TOK_P_ENDIF,"!endif",0,0,"",TP_ALL},
-{TOK_P_DEFINE,"!define",1,2,"[/date] symbol [value]",TP_ALL},
+{TOK_P_DEFINE,"!define",1,4,"([/date] symbol [value]) | (/math symbol val1 OP val2)\n    OP=(+ - * / %)",TP_ALL},
 {TOK_P_UNDEF,"!undef",1,1,"symbol [value]",TP_ALL},
 {TOK_P_ELSE,"!else",0,-1,"[if[macro][n][def] ...]",TP_ALL},
 {TOK_P_ECHO,"!echo",1,0,"message",TP_ALL},