diff --git a/src/kits/shared/Json.cpp b/src/kits/shared/Json.cpp
index 100e216313..9686266847 100644
--- a/src/kits/shared/Json.cpp
+++ b/src/kits/shared/Json.cpp
@@ -99,7 +99,7 @@ BJson::Parse(BMessage& message, BString& JSON)
 			
 			if (_Parser_ParseConstant(JSON, pos, "true")) {
 				if (builder.What() == JSON_TYPE_ARRAY)
-					key.SetToFormat("%zu", builder.CountNames());
+					key.SetToFormat("%" B_PRIu32, builder.CountNames());
 				builder.AddBool(key.String(), true);
 				key = "";
 			} else
@@ -117,7 +117,7 @@ BJson::Parse(BMessage& message, BString& JSON)
 			
 			if (_Parser_ParseConstant(JSON, pos, "false")) {
 				if (builder.What() == JSON_TYPE_ARRAY)
-					key.SetToFormat("%zu", builder.CountNames());
+					key.SetToFormat("%" B_PRIu32, builder.CountNames());
 				builder.AddBool(key.String(), false);
 				key = "";
 			} else
@@ -135,7 +135,7 @@ BJson::Parse(BMessage& message, BString& JSON)
 			
 			if (_Parser_ParseConstant(JSON, pos, "null")) {
 				if (builder.What() == JSON_TYPE_ARRAY)
-					key.SetToFormat("%zu", builder.CountNames());
+					key.SetToFormat("%" B_PRIu32, builder.CountNames());
 				builder.AddPointer(key.String(), (void*)NULL);
 				key = "";
 			} else
diff --git a/src/kits/shared/MessageBuilder.cpp b/src/kits/shared/MessageBuilder.cpp
index 2cd28e1427..e81bd3429c 100644
--- a/src/kits/shared/MessageBuilder.cpp
+++ b/src/kits/shared/MessageBuilder.cpp
@@ -62,7 +62,7 @@ status_t
 BMessageBuilder::PushObject(uint32 name)
 {
 	BString nameString;
-	nameString.SetToFormat("%zu", name);
+	nameString.SetToFormat("%" B_PRIu32, name);
 	return PushObject(nameString.String());
 }