diff --git a/ChangeLog b/ChangeLog
index 2c9172913f..551113eb7e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu May 24 14:23:35 2001  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* eval.c (rb_yield_0): need argument adjustment for C defined
+	  blocks too.
+
 Tue May 22 17:10:35 2001  K.Kosako  <kosako@sofnec.co.jp>
 
 	* variable.c (rb_alias_variable): should not allow variable
diff --git a/eval.c b/eval.c
index 651b9b5276..12baccb2d7 100644
--- a/eval.c
+++ b/eval.c
@@ -3559,6 +3559,13 @@ rb_yield_0(val, self, klass, acheck)
 	POP_TAG();
 	if (state) goto pop_state;
     }
+    else {
+	/* argument adjust for proc_call etc. */
+	if (acheck && val != Qundef &&
+	    TYPE(val) == T_ARRAY && RARRAY(val)->len == 1) {
+	    val = RARRAY(val)->ptr[0];
+	}
+    }
 
     PUSH_ITER(block->iter);
     PUSH_TAG(PROT_NONE);
diff --git a/version.h b/version.h
index d69331729f..b343db5105 100644
--- a/version.h
+++ b/version.h
@@ -1,4 +1,4 @@
 #define RUBY_VERSION "1.6.4"
-#define RUBY_RELEASE_DATE "2001-05-22"
+#define RUBY_RELEASE_DATE "2001-05-24"
 #define RUBY_VERSION_CODE 164
-#define RUBY_RELEASE_CODE 20010522
+#define RUBY_RELEASE_CODE 20010524