diff --git a/code/MD2/MD2Loader.cpp b/code/MD2/MD2Loader.cpp
index a26f70533c9..7023c0fa323 100644
--- a/code/MD2/MD2Loader.cpp
+++ b/code/MD2/MD2Loader.cpp
@@ -344,7 +344,7 @@ void MD2Importer::InternReadFile( const std::string& pFile,
         if (pcSkins->name[0])
         {
             aiString szString;
-            const size_t iLen = ::strlen(pcSkins->name);
+            const ai_uint32 iLen = (ai_uint32) ::strlen(pcSkins->name);
             ::memcpy(szString.data,pcSkins->name,iLen);
             szString.data[iLen] = '\0';
             szString.length = iLen;
diff --git a/code/MD5/MD5Parser.cpp b/code/MD5/MD5Parser.cpp
index b955e9cbce6..37490212fb7 100644
--- a/code/MD5/MD5Parser.cpp
+++ b/code/MD5/MD5Parser.cpp
@@ -235,7 +235,7 @@ bool MD5Parser::ParseSection(Section& out)
     const char* szStart = ++sz; \
 	while('\"'!=*sz)++sz; \
     const char* szEnd = (sz++); \
-    out.length = (size_t)(szEnd - szStart); \
+    out.length = (ai_uint32) (szEnd - szStart); \
     ::memcpy(out.data,szStart,out.length); \
     out.data[out.length] = '\0';
 // ------------------------------------------------------------------------------------------------
diff --git a/code/PostProcessing/ValidateDataStructure.cpp b/code/PostProcessing/ValidateDataStructure.cpp
index 712fd6943dd..501f7a9b2b2 100644
--- a/code/PostProcessing/ValidateDataStructure.cpp
+++ b/code/PostProcessing/ValidateDataStructure.cpp
@@ -958,7 +958,7 @@ void ValidateDSProcess::Validate( const aiString* pString)
 {
     if (pString->length > MAXLEN)
     {
-        ReportError("aiString::length is too large (%lu, maximum is %lu)",
+        ReportError("aiString::length is too large (%u, maximum is %lu)",
             pString->length,MAXLEN);
     }
     const char* sz = pString->data;
diff --git a/include/assimp/types.h b/include/assimp/types.h
index e0a004c92c9..8ad5680f395 100644
--- a/include/assimp/types.h
+++ b/include/assimp/types.h
@@ -274,8 +274,8 @@ struct aiString
     }
 
     /** Copy constructor */
-    aiString(const aiString& rOther) :
-        length(rOther.length)
+    aiString(const aiString& rOther)
+    : length(rOther.length)
     {
         // Crop the string to the maximum length
         length = length>=MAXLEN?MAXLEN-1:length;
@@ -285,7 +285,7 @@ struct aiString
 
     /** Constructor from std::string */
     explicit aiString(const std::string& pString) :
-        length(pString.length())
+        length( (ai_uint32) pString.length())
     {
         length = length>=MAXLEN?MAXLEN-1:length;
         memcpy( data, pString.c_str(), length);
@@ -297,15 +297,15 @@ struct aiString
         if( pString.length() > MAXLEN - 1) {
             return;
         }
-        length = pString.length();
+        length = (ai_uint32)pString.length();
         memcpy( data, pString.c_str(), length);
         data[length] = 0;
     }
 
     /** Copy a const char* to the aiString */
     void Set( const char* sz) {
-        const size_t len = ::strlen(sz);
-        if( len > MAXLEN - 1) {
+        const ai_int32 len = (ai_uint32) ::strlen(sz);
+        if( len > (ai_int32)MAXLEN - 1) {
             return;
         }
         length = len;
@@ -351,7 +351,7 @@ struct aiString
 
     /** Append a string to the string */
     void Append (const char* app)   {
-        const size_t len = ::strlen(app);
+        const ai_uint32 len = (ai_uint32) ::strlen(app);
         if (!len) {
             return;
         }