diff --git a/Changes b/Changes
index 6cefe24ee..2c30c431c 100644
--- a/Changes
+++ b/Changes
@@ -25,6 +25,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ****  Fix trace overflow on huge arrays, bug834. [Geoff Barrett]
 
+****  Fix quoted comment slashes in defines, bug845. [Adam Krolnik]
+
 
 * Verilator 3.864 2014-09-21
 
diff --git a/src/V3PreLex.h b/src/V3PreLex.h
index 17e20e6b0..1c5cf17ca 100644
--- a/src/V3PreLex.h
+++ b/src/V3PreLex.h
@@ -169,6 +169,7 @@ class V3PreLex {
     int		m_pslParenLevel;// PSL Parenthesis (){} counting, so we can find final ;
     bool	m_pslMoreNeeded;// Next // comment is really psl
     bool	m_defCmtSlash;	// /*...*/ comment in define had \ ending
+    bool	m_defQuote;	// Definition value inside quote
     string	m_defValue;	// Definition value being built.
     int		m_enterExit;	// For VL_LINE, the enter/exit level
 
@@ -181,6 +182,7 @@ class V3PreLex {
 	m_pedantic = false;
 	m_formalLevel = 0;
 	m_parenLevel = 0;
+	m_defQuote = false;
 	m_defCmtSlash = false;
 	m_tokFilelinep = filelinep;
 	m_enterExit = 0;
diff --git a/src/V3PreLex.l b/src/V3PreLex.l
index b58b67132..58191a968 100644
--- a/src/V3PreLex.l
+++ b/src/V3PreLex.l
@@ -125,7 +125,7 @@ psl		[p]sl
 <STRMODE>{backslash}{crnl}	{ linenoInc(); yymore(); }
 <STRMODE>{backslash}.	{ yymore(); }
 <STRMODE>{quote} 	{ yy_pop_state();
-			  if (LEXP->m_parenLevel || LEXP->m_formalLevel) { appendDefValue(yytext,yyleng); yyleng=0; }
+			  if (LEXP->m_parenLevel || LEXP->m_defQuote) { LEXP->m_defQuote=false; appendDefValue(yytext,yyleng); yyleng=0; }
 			  else return (VP_STRING); }
 
 	/* Stringification */
@@ -162,7 +162,7 @@ psl		[p]sl
 <DEFFORM><<EOF>>	{ linenoInc(); yy_pop_state(); yyerrorf("Unterminated ( in define formal arguments."); yyleng=0; return VP_DEFFORM; }
 <DEFFORM>{crnl}		{ linenoInc(); appendDefValue((char*)"\n",1); } /* Include return so can maintain output line count */
 <DEFFORM>[\\]{crnl}	{ linenoInc(); appendDefValue((char*)"\\\n",2); } /* Include return so can maintain output line count */
-<DEFFORM>{quote}	{ yy_push_state(STRMODE); yymore(); }  /* Legal only in default values */
+<DEFFORM>{quote}	{ LEXP->m_defQuote=true; yy_push_state(STRMODE); yymore(); }  /* Legal only in default values */
 <DEFFORM>"`\\`\""	{ appendDefValue(yytext,yyleng); }  /* Maybe illegal, otherwise in default value */
 <DEFFORM>{tickquote}	{ appendDefValue(yytext,yyleng); }  /* Maybe illegal, otherwise in default value */
 <DEFFORM>[{\[]		{ LEXP->m_formalLevel++; appendDefValue(yytext,yyleng); }
@@ -179,7 +179,8 @@ psl		[p]sl
 <DEFVAL><<EOF>>		{ linenoInc(); yy_pop_state(); yytext=(char*)"\n"; yyleng=1; return (VP_DEFVALUE); } /* Technically illegal, but people complained */
 <DEFVAL>{crnl}		{ linenoInc(); yy_pop_state(); yytext=(char*)"\n"; yyleng=1; return (VP_DEFVALUE); }
 <DEFVAL>[\\]{crnl}	{ linenoInc(); appendDefValue((char*)"\\\n",2); } /* Return, AND \ is part of define value */
-<DEFVAL>[^\/\*\n\r\\]+	|
+<DEFVAL>{quote}		{ LEXP->m_defQuote=true; yy_push_state(STRMODE); yymore(); }
+<DEFVAL>[^\/\*\n\r\\\"]+	|
 <DEFVAL>[\\][^\n\r]	|
 <DEFVAL>.		{ appendDefValue(yytext,yyleng); }
 
diff --git a/test_regress/t/t_preproc.out b/test_regress/t/t_preproc.out
index 5c918d41f..7e0bddfd2 100644
--- a/test_regress/t/t_preproc.out
+++ b/test_regress/t/t_preproc.out
@@ -788,6 +788,10 @@ module t;
  
    initial $write("GOT='%s' EXP='%s'\n", "foo `A(bar) baz", "foo `A(bar) baz");
     
+    
+    
+ 
+   initial $write("Slashed=`%s'\n", "1//2.3");
 endmodule
  
  
@@ -809,4 +813,4 @@ predef 1 1
 predef 2 2
  
 
-`line 544 "t/t_preproc.v" 2
+`line 548 "t/t_preproc.v" 2
diff --git a/test_regress/t/t_preproc.v b/test_regress/t/t_preproc.v
index 25ad54031..7137314f2 100644
--- a/test_regress/t/t_preproc.v
+++ b/test_regress/t/t_preproc.v
@@ -520,6 +520,10 @@ module t;
 `define A(name) boo name hiss
    initial $write("GOT='%s' EXP='%s'\n", `STR(`A(bar)), "foo `A(bar) baz");
 `undef A  `undef STR
+   //----
+   // bug845
+`define SLASHED "1//2.3"
+   initial $write("Slashed=`%s'\n", `SLASHED);
 endmodule
 //======================================================================
 // IEEE mandated predefines