diff --git a/Changes b/Changes
index 81a383916..120b21fc1 100644
--- a/Changes
+++ b/Changes
@@ -26,6 +26,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 **** Support for loop i++, ++i, i--, --i, bug175. [by Byron Bradley]
 
+**** Fix `define argument mis-replacing system task of same name, bug191.
+
 **** Fix Verilator core dump on wide integer divides, bug178. [Byron Bradley]
 
 * Verilator 3.720 2009/10/26
diff --git a/src/V3PreProc.cpp b/src/V3PreProc.cpp
index 074efba45..357dbf36c 100644
--- a/src/V3PreProc.cpp
+++ b/src/V3PreProc.cpp
@@ -462,6 +462,7 @@ string V3PreProcImp::defineSubst(V3DefineRef* refp) {
 	    //cout << "CH "<<*cp<<"  an "<<argName<<"\n";
 	    if (!quote) {
 		if ( isalpha(*cp) || *cp=='_'
+		     || *cp=='$' // Won't replace system functions, since no $ in argValueByName
 		     || (argName!="" && (isdigit(*cp) || *cp=='$'))) {
 		    argName += *cp;
 		    continue;
diff --git a/test_regress/t/t_preproc.out b/test_regress/t/t_preproc.out
index 50fa1e5a3..07ac975da 100644
--- a/test_regress/t/t_preproc.out
+++ b/test_regress/t/t_preproc.out
@@ -196,5 +196,11 @@ Line_Preproc_Check 144
  
  
  
+ 
 x,y)--bee  submacro has comma paren
-`line 152 "t/t_preproc.v" 2
+
+
+
+ 
+$display("bits %d %d", $bits(foo), `10);
+`line 158 "t/t_preproc.v" 2
diff --git a/test_regress/t/t_preproc.v b/test_regress/t/t_preproc.v
index 255deebf1..c5670aea4 100644
--- a/test_regress/t/t_preproc.v
+++ b/test_regress/t/t_preproc.v
@@ -146,6 +146,12 @@ Line_Preproc_Check `__LINE__
 //======================================================================
 // misparsed comma in submacro
 `define sb bee
+`define appease_emacs_paren_matcher (
 `define sa(l) x,y)
 `define sfoo(q,r) q--r
 `sfoo(`sa(el),`sb)  submacro has comma paren
+
+//======================================================================
+// bug191
+`define bug191(bits) $display("bits %d %d", $bits(foo), `bits);
+`bug191(10)