diff --git a/Makefile.in b/Makefile.in
index 0d19c7f..4dc2555 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -29,7 +29,11 @@ PROGRAMS=\
 
 all: $(PROGRAMS)
 
-PDATA_SOURCE=\
+SOURCE=\
+	base/error_state.cc \
+	\
+	caching/superblock.cc \
+	\
 	persistent-data/checksum.cc \
 	persistent-data/endian_utils.cc \
 	persistent-data/error_set.cc \
@@ -42,13 +46,7 @@ PDATA_SOURCE=\
 	persistent-data/space_map.cc \
 	persistent-data/space-maps/disk.cc \
 	persistent-data/space-maps/recursive.cc \
-	persistent-data/space-maps/careful_alloc.cc
-#PDATA_OBJECTS=$(subst .cc,.o,$(PDATA_SOURCE))
-
-SOURCE=\
-	$(PDATA_SOURCE) \
-	\
-	caching/superblock.cc \
+	persistent-data/space-maps/careful_alloc.cc \
 	\
 	thin-provisioning/device_tree.cc \
 	thin-provisioning/file_utils.cc \
@@ -66,7 +64,7 @@ SOURCE=\
 PDATA_OBJECTS=$(subst .cc,.o,$(SOURCE))
 
 CXX_PROGRAM_SOURCE=\
-	caching/check.cc \
+	caching/cache_check.cc \
 	\
 	thin-provisioning/thin_check.cc \
 	thin-provisioning/thin_dump.cc \
@@ -140,6 +138,7 @@ THIN_DUMP_SOURCE=$(SOURCE)
 THIN_REPAIR_SOURCE=$(SOURCE)
 THIN_RESTORE_SOURCE=$(SOURCE)
 THIN_CHECK_SOURCE=\
+	base/error_state.cc \
 	persistent-data/checksum.cc \
 	persistent-data/endian_utils.cc \
 	persistent-data/error_set.cc \
diff --git a/base/error_state.cc b/base/error_state.cc
new file mode 100644
index 0000000..fdb899e
--- /dev/null
+++ b/base/error_state.cc
@@ -0,0 +1,19 @@
+#include "base/error_state.h"
+
+//----------------------------------------------------------------
+
+base::error_state
+base::combine_errors(error_state lhs, error_state rhs) {
+	switch (lhs) {
+	case NO_ERROR:
+		return rhs;
+
+	case NON_FATAL:
+		return (rhs == FATAL) ? FATAL : lhs;
+
+	default:
+		return lhs;
+	}
+}
+
+//----------------------------------------------------------------
diff --git a/base/error_state.h b/base/error_state.h
new file mode 100644
index 0000000..9864f6a
--- /dev/null
+++ b/base/error_state.h
@@ -0,0 +1,18 @@
+#ifndef BASE_ERROR_STATE_H
+#define BASE_ERROR_STATE_H
+
+//----------------------------------------------------------------
+
+namespace base {
+	enum error_state {
+		NO_ERROR,
+		NON_FATAL,	// eg, lost blocks
+		FATAL		// needs fixing before pool can be activated
+	};
+
+	error_state combine_errors(error_state lhs, error_state rhs);
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/caching/check.cc b/caching/cache_check.cc
similarity index 100%
rename from caching/check.cc
rename to caching/cache_check.cc
diff --git a/thin-provisioning/thin_check.cc b/thin-provisioning/thin_check.cc
index bf27e70..acca39b 100644
--- a/thin-provisioning/thin_check.cc
+++ b/thin-provisioning/thin_check.cc
@@ -22,6 +22,7 @@
 
 #include "version.h"
 
+#include "base/error_state.h"
 #include "base/nested_output.h"
 #include "persistent-data/space-maps/core.h"
 #include "thin-provisioning/device_tree.h"
@@ -29,33 +30,13 @@
 #include "thin-provisioning/mapping_tree.h"
 #include "thin-provisioning/superblock.h"
 
+using namespace base;
 using namespace std;
 using namespace thin_provisioning;
 
 //----------------------------------------------------------------
 
 namespace {
-
-	enum error_state {
-		NO_ERROR,
-		NON_FATAL,	// eg, lost blocks
-		FATAL		// needs fixing before pool can be activated
-	};
-
-	error_state
-	combine_errors(error_state lhs, error_state rhs) {
-		switch (lhs) {
-		case NO_ERROR:
-			return rhs;
-
-		case NON_FATAL:
-			return (rhs == FATAL) ? FATAL : lhs;
-
-		default:
-			return lhs;
-		}
-	}
-
 	//--------------------------------
 
 	block_manager<>::ptr
@@ -91,7 +72,7 @@ namespace {
 			err_ = combine_errors(err_, FATAL);
 		}
 
-		error_state get_error() const {
+		base::error_state get_error() const {
 			return err_;
 		}