diff --git a/eth/rlp.nim b/eth/rlp.nim
index 855a887..ecd00a4 100644
--- a/eth/rlp.nim
+++ b/eth/rlp.nim
@@ -107,7 +107,9 @@ proc payloadOffset(self: Rlp): int =
   if isSingleByte(): 0 else: 1 + lengthBytesCount()
 
 template readAheadCheck(numberOfBytes) =
-  if position + numberOfBytes >= bytes.len: eosError()
+  # important to add nothing to the left side of the equation as `numberOfBytes`
+  # can in theory be at max size of its type already
+  if numberOfBytes >= bytes.len - position: eosError()
 
 template nonCanonicalNumberError =
   raise newException(MalformedRlpError, "Small number encoded in a non-canonical way")
@@ -138,7 +140,9 @@ proc payloadBytesCount(self: Rlp): int =
     if remainingBytes > 1 and self.bytes[self.position + 1] == 0:
       raise newException(MalformedRlpError, "Number encoded with a leading zero")
 
-    if lengthBytes > sizeof(result):
+    # check if the size is not bigger than the max that result can hold
+    if lengthBytes > sizeof(result) or
+      (lengthBytes == sizeof(result) and self.bytes[self.position + 1].int > 127):
       raise newException(UnsupportedRlpError, "Message too large to fit in memory")
 
     for i in 1 .. lengthBytes:
diff --git a/tests/rlp/cases/invalidRLPTest.json b/tests/rlp/cases/invalidRLPTest.json
index bed8b30..0b06f27 100644
--- a/tests/rlp/cases/invalidRLPTest.json
+++ b/tests/rlp/cases/invalidRLPTest.json
@@ -42,5 +42,46 @@
 	"bytesShouldBeSingleByte7F": {
 		"in": "INVALID",
 		"out": "817F"
+	},
+
+	"fakelonglist": {
+		"in": "INVALID",
+		"out": "ff7fffffffffffffffff"
+	},
+
+	"fakelonglist2": {
+		"in": "INVALID",
+		"out": "ff800000000000000000"
+	},
+
+	"fakelongblob": {
+		"in": "INVALID",
+		"out": "bf7fffffffffffffffff"
+	},
+
+	"fakelongblob2": {
+		"in": "INVALID",
+		"out": "bf800000000000000000"
+	},
+
+	"fakelongblobinlist": {
+		"in": "INVALID",
+		"out": "f2bf7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
+	},
+
+	"fakelongblobinlist2": {
+		"in": "INVALID",
+		"out": "f2bf80000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+	},
+
+	"fakelonglistinlist": {
+		"in": "INVALID",
+		"out": "f2ff7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
+	},
+
+	"fakelonglistinlist2": {
+		"in": "INVALID",
+		"out": "f2ff80000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
 	}
+
 }
diff --git a/tests/rlp/test_json_suite.nim b/tests/rlp/test_json_suite.nim
index 0f9e87c..c5d498d 100644
--- a/tests/rlp/test_json_suite.nim
+++ b/tests/rlp/test_json_suite.nim
@@ -1,8 +1,12 @@
 import
-  os, strutils,
+  os, strutils, strformat,
   util/json_testing
 
-for file in walkDirRec("tests/cases"):
+template sourceDir: string = currentSourcePath.rsplit(DirSep, 1)[0]
+
+const casesDir = &"{sourceDir}{DirSep}cases{DirSep}"
+
+for file in walkDirRec(casesDir):
   if file.endsWith("json"):
     runTests(file)
 
diff --git a/tests/rlp/util/json_testing.nim b/tests/rlp/util/json_testing.nim
index dedd6a2..a751dda 100644
--- a/tests/rlp/util/json_testing.nim
+++ b/tests/rlp/util/json_testing.nim
@@ -48,7 +48,7 @@ proc runTests*(filename: string) =
         inspectOutput = rlp.inspect(1)
         discard rlp.getType
         while rlp.hasData: discard rlp.toNodes
-      except MalformedRlpError, ValueError:
+      except MalformedRlpError, UnsupportedRlpError, ValueError:
         success = true
       if not success:
         testStatus "FAILED"