diff --git a/parse.nim b/parse.nim
index 1453273..03efa6d 100644
--- a/parse.nim
+++ b/parse.nim
@@ -48,8 +48,7 @@ proc getUntil(input: string, delimiters: openArray[char], packet: var PsycPacket
       packet.cursor = i
       break
     if not validate(input[i]):
-      raise newException(PsycSyntaxError,
-                         "invalid character '" & input[i] & "' in " & $packet.state)
+      raise newException(PsycSyntaxError, "invalid character in " & $packet.state)
 
 proc parseKeyword(input: string,
                   packet: var PsycPacket): tuple[complete: bool, value: string] =
@@ -71,7 +70,7 @@ proc parseModifierValueLength(input: string,
   if value.len() == 0:
     raise newException(PsycSyntaxError, "missing length after " & $packet.state)
   try:
-    result = (true, value.parseInt()) # may throw ValueError if invalid number
+    result = (true, value.parseInt())
   except ValueError:
     raise newException(PsycSyntaxError, "invalid length after " & $packet.state)
   if result.value < 0:
@@ -155,11 +154,10 @@ proc parseContentLength(input: string,
       result.value = -1
     else:
       try:
-        result.value = value.parseInt() # parseInt may throw ValueError if invalid number
+        result.value = value.parseInt()
       except ValueError:
-        raise newException(PsycSyntaxError, "invalid length after " & $packet.state)
-      if result.value < 0:
-        raise newException(PsycSyntaxError, "invalid length after " & $packet.state)
+        raise newException(PsycSyntaxError,
+                           $packet.state & " is not a positive integer")
 
 proc parseData(input: string,
                packet: var PsycPacket): tuple[complete: bool, value: string] =
@@ -457,4 +455,27 @@ suite "parser tests":
     check(packet.state == ParseState.Complete)
     check(packet.data == "Hello Alice!")
 
+  test "invalid character in keyword":
+    let input = ":\0\n"
+    try:
+      (needMore, unparsed) = parse(input, packet)
+    except PsycSyntaxError:
+      check(getCurrentExceptionMsg() == "invalid character in RoutingModifierName")
+
+  test "empty keyword":
+    let input = ":\n"
+    try:
+      (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:
+      (needMore, unparsed) = parse(input, packet)
+    except PsycSyntaxError:
+      check(getCurrentExceptionMsg() == "ContentLength is not a positive integer")
+
   echo "parser tests completed"