diff --git a/Makefile b/Makefile
index 06bafdf8f..e3f3134e4 100644
--- a/Makefile
+++ b/Makefile
@@ -79,10 +79,10 @@ endif
 all: lib/libxgboost.a $(XGBOOST_DYLIB) xgboost
 
 $(DMLC_CORE)/libdmlc.a: $(wildcard $(DMLC_CORE)/src/*.cc $(DMLC_CORE)/src/*/*.cc)
-	+ cd $(DMLC_CORE); make libdmlc.a config=$(ROOTDIR)/$(config); cd $(ROOTDIR)
+	+ cd $(DMLC_CORE); $(MAKE) libdmlc.a config=$(ROOTDIR)/$(config); cd $(ROOTDIR)
 
 $(RABIT)/lib/$(LIB_RABIT): $(wildcard $(RABIT)/src/*.cc)
-	+ cd $(RABIT); make lib/$(LIB_RABIT); cd $(ROOTDIR)
+	+ cd $(RABIT); $(MAKE) lib/$(LIB_RABIT); cd $(ROOTDIR)
 
 jvm: jvm-packages/lib/libxgboost4j.so
 
@@ -137,8 +137,8 @@ clean:
 	$(RM) -rf build build_plugin lib bin *~ */*~ */*/*~ */*/*/*~ */*.o */*/*.o */*/*/*.o xgboost
 
 clean_all: clean
-	cd $(DMLC_CORE); make clean; cd $(ROODIR)
-	cd $(RABIT); make clean; cd $(ROODIR)
+	cd $(DMLC_CORE); $(MAKE) clean; cd $(ROODIR)
+	cd $(RABIT); $(MAKE) clean; cd $(ROODIR)
 
 doxygen:
 	doxygen doc/Doxyfile
@@ -150,7 +150,7 @@ pypack: ${XGBOOST_DYLIB}
 
 # Script to make a clean installable R package.
 Rpack:
-	make clean_all
+	$(MAKE) clean_all
 	rm -rf xgboost xgboost*.tar.gz
 	cp -r R-package xgboost
 	rm -rf xgboost/src/*.o xgboost/src/*.so xgboost/src/*.dll
@@ -172,12 +172,12 @@ Rpack:
 	cp xgboost/src/Makevars xgboost/src/Makevars.win
 
 Rbuild:
-	make Rpack
+	$(MAKE) Rpack
 	R CMD build --no-build-vignettes xgboost
 	rm -rf xgboost
 
 Rcheck:
-	make Rbuild
+	$(MAKE) Rbuild
 	R CMD check  xgboost*.tar.gz
 
 -include build/*.d
diff --git a/doc/jvm/index.md b/doc/jvm/index.md
index a6e731c54..e9a16477e 100644
--- a/doc/jvm/index.md
+++ b/doc/jvm/index.md
@@ -13,6 +13,8 @@ Before you install XGBoost4J, you need to define environment variable `JAVA_HOME
 
 After your `JAVA_HOME` is defined correctly, it is as simple as run `mvn package` under jvm-packages directory to install XGBoost4J.
 
+NOTE: XGBoost4J requires to run with Spark 1.6 or newer 
+
 Contents
 --------
 * [Java Overview Tutorial](java_intro.md)
diff --git a/include/xgboost/c_api.h b/include/xgboost/c_api.h
index 68f35ace9..1598aac3b 100644
--- a/include/xgboost/c_api.h
+++ b/include/xgboost/c_api.h
@@ -266,7 +266,7 @@ XGB_DLL int XGDMatrixNumCol(DMatrixHandle handle,
  * \param out handle to the result booster
  * \return 0 when success, -1 when failure happens
  */
-XGB_DLL int XGBoosterCreate(void* dmats[],
+XGB_DLL int XGBoosterCreate(const DMatrixHandle dmats[],
                             bst_ulong len,
                             BoosterHandle *out);
 /*!
diff --git a/src/c_api/c_api.cc b/src/c_api/c_api.cc
index d0ea7815b..6ee4f93dc 100644
--- a/src/c_api/c_api.cc
+++ b/src/c_api/c_api.cc
@@ -463,7 +463,7 @@ int XGDMatrixNumCol(const DMatrixHandle handle,
 }
 
 // xgboost implementation
-int XGBoosterCreate(DMatrixHandle dmats[],
+int XGBoosterCreate(const DMatrixHandle dmats[],
                     bst_ulong len,
                     BoosterHandle *out) {
   API_BEGIN();