diff --git a/parse.nim b/parse.nim
index 03efa6d..a17e921 100644
--- a/parse.nim
+++ b/parse.nim
@@ -29,6 +29,10 @@ type
 
   PsycSyntaxError = object of Exception
 
+  InvalidModifierName = object of PsycSyntaxError
+  InvalidModifierValue = object of PsycSyntaxError
+  InvalidContentLength = object of PsycSyntaxError
+
   Validator = proc(c: char): bool
 
 proc validateTrue(c: char): bool = true
@@ -48,7 +52,7 @@ proc getUntil(input: string, delimiters: openArray[char], packet: var PsycPacket
       packet.cursor = i
       break
     if not validate(input[i]):
-      raise newException(PsycSyntaxError, "invalid character in " & $packet.state)
+      raise newException(InvalidModifierName, "invalid character in " & $packet.state)
 
 proc parseKeyword(input: string,
                   packet: var PsycPacket): tuple[complete: bool, value: string] =
@@ -58,7 +62,8 @@ proc parseKeyword(input: string,
   if result.complete:
     packet.cursor.inc()
     if result.value.len() == 0 or result.value[0] != '_':
-      raise newException(PsycSyntaxError, $packet.state & " does not start with '_'")
+      raise newException(InvalidModifierName,
+                         $packet.state & " does not start with '_'")
 
 proc parseModifierValueLength(input: string,
                               packet: var PsycPacket): tuple[complete: bool,
@@ -68,13 +73,13 @@ proc parseModifierValueLength(input: string,
     return (false, -1)
   packet.cursor.inc()
   if value.len() == 0:
-    raise newException(PsycSyntaxError, "missing length after " & $packet.state)
+    raise newException(InvalidModifierValue, "missing length of binary-arg")
   try:
     result = (true, value.parseInt())
   except ValueError:
-    raise newException(PsycSyntaxError, "invalid length after " & $packet.state)
+    raise newException(InvalidModifierValue, "invalid length of binary-arg")
   if result.value < 0:
-    raise newException(PsycSyntaxError, "invalid length after " & $packet.state)
+    raise newException(InvalidModifierValue, "invalid length of binary-arg")
 
 proc parseModifierName(input: string,
                        packet: var PsycPacket): tuple[complete: bool,
@@ -84,15 +89,12 @@ proc parseModifierName(input: string,
   if packet.cursor == input.high():
     result.complete = false
     return 
-  if input[packet.cursor] == '\n':
-    packet.cursor.inc()
-    return (true, '\0', nil)
   result.op = input[packet.cursor]
   packet.cursor.inc()
   if result.op == '?':
     if input[packet.cursor] != '\n':
-      raise newException(PsycSyntaxError,
-                         $packet.state & " has invalid operator '?'")
+      raise newException(InvalidModifierName,
+                         "state sync modifier '?' must not have a name")
     result.complete = true
     return 
   (result.complete, result.name) = parseKeyword(input, packet)
@@ -101,10 +103,13 @@ proc parseModifierName(input: string,
     return
   # the following separator must either be ' ' (binary-arg) or '\t' (simple-arg)
   if input[packet.cursor - 1] == ' ':
+    if packet.state != ParseState.EntityModifierName:
+      raise newException(InvalidModifierValue,
+                         "binary-arg not allowed in routing modifier")
     (result.complete, packet.remainingPartLen) = parseModifierValueLength(input,
                                                                           packet)
   elif input[packet.cursor - 1] != '\t':
-    raise newException(PsycSyntaxError, $packet.state & " has invalid separator")
+    raise newException(InvalidModifierValue, "modifier has invalid separator")
  
 proc parseMethod(input: string, packet: var PsycPacket): tuple[complete: bool,
                                                                value: string] =
@@ -134,8 +139,8 @@ proc parseModifierValue(input: string,
   if result.complete:
     result.value = input[packet.cursor .. packet.cursor + packet.remainingPartLen - 1]
     if input[packet.cursor + packet.remainingPartLen] != '\n':
-      raise newException(PsycSyntaxError,
-                         $packet.state & " is missing '\n' after binary-arg")
+      raise newException(InvalidModifierValue,
+                         $packet.state & " is missing '\\n' after binary-arg")
     packet.cursor += result.value.len() + 1
     packet.remainingPartLen = -1
   else:
@@ -156,7 +161,7 @@ proc parseContentLength(input: string,
       try:
         result.value = value.parseInt()
       except ValueError:
-        raise newException(PsycSyntaxError,
+        raise newException(InvalidContentLength,
                            $packet.state & " is not a positive integer")
 
 proc parseData(input: string,
@@ -457,25 +462,32 @@ suite "parser tests":
 
   test "invalid character in keyword":
     let input = ":\0\n"
-    try:
+    expect(InvalidModifierName):
       (needMore, unparsed) = parse(input, packet)
-    except PsycSyntaxError:
-      check(getCurrentExceptionMsg() == "invalid character in RoutingModifierName")
 
   test "empty keyword":
     let input = ":\n"
-    try:
+    expect(InvalidModifierName):
+      (needMore, unparsed) = parse(input, packet)
+
+  test "routing modifier with binary-arg":
+    let input = ":_test 4\ttest\n"
+    expect(InvalidModifierValue):
+      (needMore, unparsed) = parse(input, packet)
+
+  test "binary-arg without length":
+    let input = "\n:_test \t"
+    (needMore, unparsed) = parse(input, packet)
+    (needMore, unparsed) = parse(input, packet)
+    check(packet.state == ParseState.EntityModifierName)
+    expect(InvalidModifierValue):
       (needMore, unparsed) = parse(input, packet)
-    except PsycSyntaxError:
-      check(getCurrentExceptionMsg() == "RoutingModifierName does not start with '_'")
 
   test "invalid content length":
     let input = "abc\n"
     (needMore, unparsed) = parse(input, packet)
     check(packet.state == ParseState.ContentLength)
-    try:
+    expect(InvalidContentLength):
       (needMore, unparsed) = parse(input, packet)
-    except PsycSyntaxError:
-      check(getCurrentExceptionMsg() == "ContentLength is not a positive integer")
 
   echo "parser tests completed"