diff --git a/GNUmakefile b/GNUmakefile
index 7946d27..b75f64b 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -22,7 +22,7 @@ ifeq (${MAKECMDGOALS},config)
     config: make.inc
 
     make.inc: force
-else ifneq ($(findstring clean,${MAKECMDGOALS}),clean)
+else ifneq (clean,${findstring clean,${MAKECMDGOALS}})
     # For `make clean` or `make distclean`, don't include make.inc,
     # which could generate it. Otherwise, include make.inc.
     include make.inc
@@ -69,7 +69,7 @@ ldflags_shared = -shared
 # auto-detect OS
 # $OSTYPE may not be exported from the shell, so echo it
 ostype := ${shell echo $${OSTYPE}}
-ifneq ($(findstring darwin, ${ostype}),)
+ifneq (,${findstring darwin, ${ostype}})
     # MacOS is darwin
     macos = 1
     # MacOS needs shared library's path set, and shared library version.
@@ -271,13 +271,20 @@ distclean: clean
 #-------------------------------------------------------------------------------
 # debugging
 echo:
-	@echo "ostype        = '${ostype}'"
+	@echo "---------- Options"
 	@echo "static        = '${static}'"
+	@echo "prefix        = '${prefix}'"
+	@echo "abs_prefix    = '${abs_prefix}'"
+	@echo
+	@echo "---------- Internal variables"
+	@echo "ostype        = '${ostype}'"
+	@echo "macos         = '${macos}'"
 	@echo "id            = '${id}'"
 	@echo "last_id       = '${last_id}'"
 	@echo "abi_version   = '${abi_version}'"
 	@echo "soversion     = '${soversion}'"
 	@echo
+	@echo "---------- Libraries"
 	@echo "lib_name      = ${lib_name}"
 	@echo "lib_a         = ${lib_a}"
 	@echo "lib_so        = ${lib_so}"
@@ -297,9 +304,11 @@ echo:
 	@echo
 	@echo "dep           = ${dep}"
 	@echo
+	@echo "---------- C++ compiler"
 	@echo "CXX           = ${CXX}"
 	@echo "CXXFLAGS      = ${CXXFLAGS}"
 	@echo
+	@echo "---------- Link flags"
 	@echo "LD            = ${LD}"
 	@echo "LDFLAGS       = ${LDFLAGS}"
 	@echo "LIBS          = ${LIBS}"