diff --git a/NEWS b/NEWS
index f594207f58..d075d4637b 100644
--- a/NEWS
+++ b/NEWS
@@ -255,6 +255,12 @@ New Functionality
   semi-present in previous versions of Bro, but required constants as as
   its operands; now you can use any pattern-valued expressions.
 
+- You can now specify that a pattern should be match in a case-insensitive
+  fashion by adding 'i' to the end of its specification.  So for example
+  /fOO/i == "Foo" yields T, as does /fOO/i in "xFoObar".  Characters
+  enclosed in quotes however keep their casing, so /"fOO"/i in "xFoObar"
+  yields F, though it yields T for "xfOObar".
+
 Changed Functionality
 ---------------------
 
diff --git a/src/RE.cc b/src/RE.cc
index 4d26ce2423..4e29fa8e92 100644
--- a/src/RE.cc
+++ b/src/RE.cc
@@ -102,6 +102,19 @@ void Specific_RE_Matcher::AddPat(const char* new_pat,
 	pattern_text = s;
 	}
 
+void Specific_RE_Matcher::MakeCaseInsensitive()
+	{
+	const char fmt[] = "(+i %s)";
+	int n = strlen(pattern_text) + strlen(fmt);
+
+	char* s = new char[n + 5 /* slop */];
+
+	safe_snprintf(s, n + 5, fmt, pattern_text);
+
+	delete [] pattern_text;
+	pattern_text = s;
+	}
+
 int Specific_RE_Matcher::Compile(int lazy)
 	{
 	if ( ! pattern_text )
@@ -444,6 +457,12 @@ void RE_Matcher::AddPat(const char* new_pat)
 	re_exact->AddPat(new_pat);
 	}
 
+void RE_Matcher::MakeCaseInsensitive()
+	{
+	re_anywhere->MakeCaseInsensitive();
+	re_exact->MakeCaseInsensitive();
+	}
+
 int RE_Matcher::Compile(int lazy)
 	{
 	return re_anywhere->Compile(lazy) && re_exact->Compile(lazy);
diff --git a/src/RE.h b/src/RE.h
index 056c0d2183..06b0699864 100644
--- a/src/RE.h
+++ b/src/RE.h
@@ -54,6 +54,8 @@ public:
 
 	void AddPat(const char* pat);
 
+	void MakeCaseInsensitive();
+
 	void SetPat(const char* pat)	{ pattern_text = copy_string(pat); }
 
 	int Compile(int lazy = 0);
@@ -178,6 +180,9 @@ public:
 
 	void AddPat(const char* pat);
 
+	// Makes the matcher as specified to date case-insensitive.
+	void MakeCaseInsensitive();
+
 	int Compile(int lazy = 0);
 
 	// Returns true if s exactly matches the pattern, false otherwise.
diff --git a/src/input.h b/src/input.h
index 3d0caa459a..230a10073a 100644
--- a/src/input.h
+++ b/src/input.h
@@ -23,7 +23,6 @@ extern void add_input_file_at_front(const char* file);
 extern void add_to_name_list(char* s, char delim, name_list& nl);
 
 extern void begin_RE();
-extern void end_RE();
 
 extern void do_atif(Expr* expr);
 extern void do_atifdef(const char* id);
diff --git a/src/parse.y b/src/parse.y
index 34d6f31373..25b6c17873 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -14,7 +14,7 @@
 %token TOK_DOUBLE TOK_ELSE TOK_ENUM TOK_EVENT TOK_EXPORT TOK_FALLTHROUGH
 %token TOK_FILE TOK_FOR TOK_FUNCTION TOK_GLOBAL TOK_HOOK TOK_ID TOK_IF TOK_INT
 %token TOK_INTERVAL TOK_LIST TOK_LOCAL TOK_MODULE
-%token TOK_NEXT TOK_OF TOK_OPAQUE TOK_PATTERN TOK_PATTERN_TEXT
+%token TOK_NEXT TOK_OF TOK_OPAQUE TOK_PATTERN TOK_PATTERN_END TOK_PATTERN_TEXT
 %token TOK_PORT TOK_PRINT TOK_RECORD TOK_REDEF
 %token TOK_REMOVE_FROM TOK_RETURN TOK_SCHEDULE TOK_SET
 %token TOK_STRING TOK_SUBNET TOK_SWITCH TOK_TABLE
@@ -52,7 +52,7 @@
 %left '$' '[' ']' '(' ')' TOK_HAS_FIELD TOK_HAS_ATTR
 %nonassoc TOK_AS TOK_IS
 
-%type <b> opt_no_test opt_no_test_block opt_deprecated
+%type <b> opt_no_test opt_no_test_block opt_deprecated TOK_PATTERN_END
 %type <str> TOK_ID TOK_PATTERN_TEXT
 %type <id> local_id global_id def_global_id event_id global_or_event_id resolve_id begin_func case_type
 %type <id_l> local_id_list case_type_list
@@ -723,13 +723,16 @@ expr:
 			$$ = new ConstExpr($1);
 			}
 
-	|	'/' { begin_RE(); } TOK_PATTERN_TEXT { end_RE(); } '/'
+	|	'/' { begin_RE(); } TOK_PATTERN_TEXT TOK_PATTERN_END
 			{
 			set_location(@3);
 
 			RE_Matcher* re = new RE_Matcher($3);
 			delete [] $3;
 
+			if ( $4 )
+				re->MakeCaseInsensitive();
+
 			re->Compile();
 			$$ = new ConstExpr(new PatternVal(re));
 			}
diff --git a/src/re-parse.y b/src/re-parse.y
index 3847c06f29..6834836f28 100644
--- a/src/re-parse.y
+++ b/src/re-parse.y
@@ -11,11 +11,13 @@
 int csize = 256;
 int syntax_error = 0;
 
+int is_letter(int sym);
+int cupper(int sym);
 int clower(int sym);
 void yyerror(const char msg[]);
 %}
 
-%token TOK_CHAR TOK_NUMBER TOK_CCL TOK_CCE
+%token TOK_CHAR TOK_NUMBER TOK_CCL TOK_CCE TOK_CASE_INSENSITIVE
 
 %union {
 	int int_val;
@@ -126,12 +128,11 @@ singleton	:  singleton '*'
 		|  '(' re ')'
 			{ $$ = $2; }
 
+		|  TOK_CASE_INSENSITIVE re ')'
+			{ $$ = $2; case_insensitive = 0; }
+
 		|  TOK_CHAR
-			{
-			if ( case_insensitive && $1 >= 'A' && $1 <= 'Z' )
-				$1 = clower($1);
-			$$ = new NFA_Machine(new NFA_State($1, rem->EC()));
-			}
+			{ $$ = new NFA_Machine(new NFA_State($1, rem->EC())); }
 
 		|  '^'
 			{
@@ -158,17 +159,29 @@ full_ccl	:  '[' ccl ']'
 
 ccl		:  ccl TOK_CHAR '-' TOK_CHAR
 			{
-			if ( case_insensitive )
-				{
-				if ( $2 >= 'A' && $2 <= 'Z' )
-					$2 = clower($2);
-				if ( $4 >= 'A' && $4 <= 'Z' )
-					$4 = clower($4);
-				}
-
 			if ( $2 > $4 )
 				synerr("negative range in character class");
 
+			else if ( case_insensitive &&
+				  (is_letter($2) || is_letter($4)) )
+				{
+				if ( is_letter($2) && is_letter($4) &&
+				     isupper($2) == isupper($4) )
+					{ // Compatible range, do both versions
+					int l2 = tolower($2);
+					int l4 = tolower($4);
+
+					for ( int i = l2; i<= l4; ++i )
+						{
+						$1->Add(i);
+						$1->Add(toupper(i));
+						}
+					}
+
+				else
+					synerr("ambiguous case-insensitive character class");
+				}
+
 			else
 				{
 				for ( int i = $2; i <= $4; ++i )
@@ -178,10 +191,13 @@ ccl		:  ccl TOK_CHAR '-' TOK_CHAR
 
 		|  ccl TOK_CHAR
 			{
-			if ( case_insensitive && $2 >= 'A' && $2 <= 'Z' )
-				$2 = clower($2);
-
-			$1->Add($2);
+			if ( case_insensitive && is_letter($2) )
+				{
+				$1->Add(clower($2));
+				$1->Add(cupper($2));
+				}
+			else
+				$1->Add($2);
 			}
 
 		|  ccl ccl_expr
@@ -200,9 +216,10 @@ ccl_expr:	   TOK_CCE
 
 string		:  string TOK_CHAR
 			{
-			if ( case_insensitive && $2 >= 'A' && $2 <= 'Z' )
-				$2 = clower($2);
-
+			// Even if case-insensitivity is set,
+			// leave this alone; that provides a way
+			// of "escaping" out of insensitivity
+			// if needed.
 			$1->AppendState(new NFA_State($2, rem->EC()));
 			}
 
@@ -211,6 +228,16 @@ string		:  string TOK_CHAR
 		;
 %%
 
+int is_letter(int sym)
+	{
+	return isascii(sym) && (islower(sym) || isupper(sym));
+	}
+
+int cupper(int sym)
+	{
+	return (isascii(sym) && islower(sym)) ?  toupper(sym) : sym;
+	}
+
 int clower(int sym)
 	{
 	return (isascii(sym) && isupper(sym)) ?  tolower(sym) : sym;
diff --git a/src/re-scan.l b/src/re-scan.l
index 8bd00c8bba..70bafd5649 100644
--- a/src/re-scan.l
+++ b/src/re-scan.l
@@ -114,6 +114,25 @@ CCL_EXPR	("[:"[[:alpha:]]+":]")
 				}
 			}
 
+	"(+i"[ \t]*	case_insensitive = 1; return TOK_CASE_INSENSITIVE;
+
+	[a-zA-Z]	{
+			if ( case_insensitive )
+				{
+				char c = yytext[0];	// unput trashes yytext!
+				// Push back the character inside a CCL,
+				// so the parser can then expand it.
+				unput(']');
+				unput(c);
+				unput('[');
+				}
+			else
+				{
+				yylval.int_val = yytext[0];
+				return TOK_CHAR;
+				}
+			}
+
 	[|*+?.(){}]	return yytext[0];
 	.		yylval.int_val = yytext[0]; return TOK_CHAR;
 	\n		return 0;	// treat as end of pattern
@@ -157,7 +176,7 @@ CCL_EXPR	("[:"[[:alpha:]]+":]")
 	"[:upper:]"	{
 			BEGIN(SC_CCL);
 			yylval.cce_val =
-				case_insensitive ? my_isupper : my_islower;
+				case_insensitive ? my_islower : my_isupper;
 			return TOK_CCE;
 			}
 
diff --git a/src/scan.l b/src/scan.l
index 3bbf6ec999..24e0547bfc 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -554,7 +554,19 @@ F	RET_CONST(new Val(false, TYPE_BOOL))
 	return TOK_PATTERN_TEXT;
 	}
 
-<RE>[/\\\n]	return yytext[0];
+<RE>"/"	{
+	BEGIN(INITIAL);
+	yylval.b = false;
+	return TOK_PATTERN_END;
+	}
+
+<RE>"/i"	{
+	BEGIN(INITIAL);
+	yylval.b = true;
+	return TOK_PATTERN_END;
+	}
+
+<RE>[\\\n]	return yytext[0];	// should cause a parse error
 
 <*>.	reporter->Error("unrecognized character - %s", yytext);