diff --git a/piclib/CMakeLists.txt b/piclib/CMakeLists.txt
index 008e5ad5..c31da069 100644
--- a/piclib/CMakeLists.txt
+++ b/piclib/CMakeLists.txt
@@ -9,7 +9,6 @@ list(APPEND PICLIB_SCHEME_LIBS
   ${PROJECT_SOURCE_DIR}/piclib/picrin/test.scm
 
   ${PROJECT_SOURCE_DIR}/piclib/scheme/base.scm
-
   ${PROJECT_SOURCE_DIR}/piclib/scheme/cxr.scm
   ${PROJECT_SOURCE_DIR}/piclib/scheme/read.scm
   ${PROJECT_SOURCE_DIR}/piclib/scheme/write.scm
@@ -22,7 +21,6 @@ list(APPEND PICLIB_SCHEME_LIBS
   ${PROJECT_SOURCE_DIR}/piclib/scheme/process-context.scm
   ${PROJECT_SOURCE_DIR}/piclib/scheme/time.scm
   ${PROJECT_SOURCE_DIR}/piclib/scheme/r5rs.scm
-  ${PROJECT_SOURCE_DIR}/piclib/scheme/null.scm
 
   ${PROJECT_SOURCE_DIR}/piclib/srfi/1.scm
   ${PROJECT_SOURCE_DIR}/piclib/srfi/8.scm
diff --git a/piclib/scheme/null.scm b/piclib/scheme/null.scm
deleted file mode 100644
index a949473e..00000000
--- a/piclib/scheme/null.scm
+++ /dev/null
@@ -1,12 +0,0 @@
-(define-library (scheme null)
-  (import (scheme base))
-  (export define
-          lambda
-          if
-          quote
-          quasiquote
-          unquote
-          unquote-splicing
-          begin
-          set!
-          define-syntax))
diff --git a/piclib/scheme/r5rs.scm b/piclib/scheme/r5rs.scm
index f3b1c563..9baebe65 100644
--- a/piclib/scheme/r5rs.scm
+++ b/piclib/scheme/r5rs.scm
@@ -9,6 +9,19 @@
           (scheme eval)
           (scheme load))
 
+  (define-library (scheme null)
+    (import (scheme base))
+    (export define
+            lambda
+            if
+            quote
+            quasiquote
+            unquote
+            unquote-splicing
+            begin
+            set!
+            define-syntax))
+
   (define (null-environment n)
     (if (not (= n 5))
         (error "unsupported environment version" n)