diff --git a/lib/filesystem/CMemoryBuffer.cpp b/lib/filesystem/CMemoryBuffer.cpp
index 39b25dc9c..849502e7a 100644
--- a/lib/filesystem/CMemoryBuffer.cpp
+++ b/lib/filesystem/CMemoryBuffer.cpp
@@ -15,7 +15,7 @@
 CMemoryBuffer::CMemoryBuffer():
 	position(0)
 {
-	
+	buffer.reserve(4096);
 }
 
 si64 CMemoryBuffer::write(const ui8 * data, si64 size)
@@ -48,7 +48,7 @@ si64 CMemoryBuffer::read(ui8 * data, si64 size)
 si64 CMemoryBuffer::seek(si64 position)
 {
 	this->position = position;
-	if (this->position >=getSize())
+	if (this->position >getSize())
 		this->position = getSize();
 	return this->position;
 }
diff --git a/lib/filesystem/MinizipExtensions.cpp b/lib/filesystem/MinizipExtensions.cpp
index 8057a907f..5810babe9 100644
--- a/lib/filesystem/MinizipExtensions.cpp
+++ b/lib/filesystem/MinizipExtensions.cpp
@@ -65,16 +65,24 @@ long ZCALLBACK CIOApi::seekFileProxy(voidpf  opaque, voidpf stream, ZPOS64_T off
     switch (origin)
     {
     case ZLIB_FILEFUNC_SEEK_CUR :
-        actualStream->skip(offset);//TODO: should we check actual skipped? 
+        if(actualStream->skip(offset) != offset)
+			ret = -1;
         break;
-    case ZLIB_FILEFUNC_SEEK_END :
-    	actualStream->seek(actualStream->getSize() - offset);
+    case ZLIB_FILEFUNC_SEEK_END:
+    	{
+    		const si64 pos = actualStream->getSize() - offset;
+    		if(actualStream->seek(pos) != pos)
+				ret = -1;
+    	}    	
         break;
     case ZLIB_FILEFUNC_SEEK_SET :
-    	actualStream->seek(offset);
+		if(actualStream->seek(offset) != offset)
+			ret = -1;
         break;
     default: ret = -1;
     }
+    if(ret == -1)
+		logGlobal->error("CIOApi::seekFileProxy: seek failed");			
     return ret;
 }
 
diff --git a/lib/mapping/MapFormatJson.cpp b/lib/mapping/MapFormatJson.cpp
index 027719301..285393236 100644
--- a/lib/mapping/MapFormatJson.cpp
+++ b/lib/mapping/MapFormatJson.cpp
@@ -213,6 +213,7 @@ void CMapLoaderJson::readHeader()
 	
 	static const std::map<std::string, ui8> difficultyMap =
 	{
+		{"", 1},
 		{"EASY", 0},
 		{"NORMAL", 1}, 
 		{"HARD", 2}, 
diff --git a/test/CMapFormatTest.cpp b/test/CMapFormatTest.cpp
index c37352e40..6d9d9353d 100644
--- a/test/CMapFormatTest.cpp
+++ b/test/CMapFormatTest.cpp
@@ -55,39 +55,32 @@ BOOST_GLOBAL_FIXTURE(CMapTestFixture);
 
 BOOST_AUTO_TEST_CASE(CMapFormatVCMI_Simple)
 {
-	try
+	logGlobal->info("CMapFormatVCMI_Simple start");
+	CMemoryBuffer serializeBuffer;
 	{
-		logGlobal->info("CMapFormatVCMI_Simple start");
-		CMemoryBuffer serializeBuffer;
-		{
-			CMapSaverJson saver(&serializeBuffer);
-			saver.saveMap(initialMap);
-		}
-		
-		#if 1
-		{
-			std::ofstream tmp((VCMIDirs::get().userDataPath()/"temp.zip").string());
-			tmp.write((const char *)&serializeBuffer.getBuffer()[0],serializeBuffer.getSize());
-			tmp.flush();
-		}
-		
-		
-		#endif // 1
-		
-		serializeBuffer.seek(0);
-		{
-			CMapLoaderJson loader(&serializeBuffer);
-			std::unique_ptr<CMap> serialized = loader.loadMap();
-
-			MapComparer c;
-			c(initialMap, serialized);
-		}
-
-		logGlobal->info("CMapFormatVCMI_Simple finish");
+		CMapSaverJson saver(&serializeBuffer);
+		saver.saveMap(initialMap);
 	}
-	catch(...)
+	
+	#if 1
 	{
-		handleException();
-		BOOST_FAIL("Test case crashed");
+		auto path = VCMIDirs::get().userDataPath()/"temp.zip";
+		boost::filesystem::remove(path);
+		boost::filesystem::ofstream tmp(path);
+		tmp.write((const char *)serializeBuffer.getBuffer().data(),serializeBuffer.getSize());
 	}
+	
+	
+	#endif // 1
+	
+	serializeBuffer.seek(0);
+	{
+		CMapLoaderJson loader(&serializeBuffer);
+		std::unique_ptr<CMap> serialized = loader.loadMap();
+
+		MapComparer c;
+		c(serialized, initialMap);
+	}
+
+	logGlobal->info("CMapFormatVCMI_Simple finish");
 }
diff --git a/test/CMemoryBufferTest.cpp b/test/CMemoryBufferTest.cpp
new file mode 100644
index 000000000..a4935be51
--- /dev/null
+++ b/test/CMemoryBufferTest.cpp
@@ -0,0 +1,52 @@
+
+/*
+ * CMemoryBufferTest.cpp, part of VCMI engine
+ *
+ * Authors: listed in file AUTHORS in main folder
+ *
+ * License: GNU General Public License v2.0 or later
+ * Full text of license available in license.txt file, in main folder
+ *
+ */
+#include "StdInc.h"
+
+#include <boost/test/unit_test.hpp>
+
+#include "../lib/filesystem/CMemoryBuffer.h"
+
+
+struct CMemoryBufferFixture
+{
+	CMemoryBuffer subject;
+};
+
+BOOST_FIXTURE_TEST_CASE(CMemoryBuffer_Empty, CMemoryBufferFixture)
+{
+	BOOST_REQUIRE_EQUAL(0, subject.tell());
+	BOOST_REQUIRE_EQUAL(0, subject.getSize());
+	
+	si32 dummy = 1337;
+	
+	auto ret = subject.read((ui8 *)&dummy, sizeof(si32));
+	
+	BOOST_CHECK_EQUAL(0, ret);	
+	BOOST_CHECK_EQUAL(1337, dummy);
+	BOOST_CHECK_EQUAL(0, subject.tell());
+}
+
+BOOST_FIXTURE_TEST_CASE(CMemoryBuffer_Write, CMemoryBufferFixture)
+{
+	const si32 initial = 1337;
+	
+	subject.write((const ui8 *)&initial, sizeof(si32));
+	
+	BOOST_CHECK_EQUAL(4, subject.tell());
+	subject.seek(0);
+	BOOST_CHECK_EQUAL(0, subject.tell());
+	
+	si32 current = 0;
+	auto ret = subject.read((ui8 *)&current, sizeof(si32));
+	BOOST_CHECK_EQUAL(sizeof(si32), ret);	
+	BOOST_CHECK_EQUAL(initial, current);
+	BOOST_CHECK_EQUAL(4, subject.tell());	
+}
diff --git a/test/MapComparer.cpp b/test/MapComparer.cpp
index 2ba2878fb..7e0544c6f 100644
--- a/test/MapComparer.cpp
+++ b/test/MapComparer.cpp
@@ -82,7 +82,7 @@ void MapComparer::compare()
 {
 	BOOST_REQUIRE_NE((void *) actual, (void *) expected); //should not point to the same object
 	BOOST_REQUIRE_MESSAGE(actual != nullptr, "Actual map is not defined");
-	BOOST_REQUIRE_MESSAGE(actual != nullptr, "Expected map is not defined");
+	BOOST_REQUIRE_MESSAGE(expected != nullptr, "Expected map is not defined");
 
 	compareHeader();
 	compareOptions();
diff --git a/test/Test.cbp b/test/Test.cbp
index 6665380f5..d9fdb6e93 100644
--- a/test/Test.cbp
+++ b/test/Test.cbp
@@ -60,6 +60,7 @@
 		</Linker>
 		<Unit filename="CMapEditManagerTest.cpp" />
 		<Unit filename="CMapFormatTest.cpp" />
+		<Unit filename="CMemoryBufferTest.cpp" />
 		<Unit filename="CVcmiTestConfig.cpp" />
 		<Unit filename="CVcmiTestConfig.h" />
 		<Unit filename="MapComparer.cpp" />