diff --git a/spec/ruby/optional/capi/ext/mri.h b/spec/ruby/optional/capi/ext/mri.h
index 7697403fba..b529d0d951 100644
--- a/spec/ruby/optional/capi/ext/mri.h
+++ b/spec/ruby/optional/capi/ext/mri.h
@@ -24,7 +24,6 @@
 #undef HAVE_STR2CSTR
 #undef HAVE_RB_STR2CSTR
 #undef HAVE_RB_SET_KCODE
-#undef HAVE_RB_PROC_NEW
 #endif
 
 /* RubySpec assumes following are public API */
diff --git a/spec/ruby/optional/capi/ext/proc_spec.c b/spec/ruby/optional/capi/ext/proc_spec.c
index 41f65f5766..6c59a90d8c 100644
--- a/spec/ruby/optional/capi/ext/proc_spec.c
+++ b/spec/ruby/optional/capi/ext/proc_spec.c
@@ -8,34 +8,45 @@ extern "C" {
 #endif
 
 #ifdef HAVE_RB_PROC_NEW
-VALUE proc_spec_concat_func(VALUE args) {
-  int i;
-  char buffer[500] = {0};
-  for(i = 0; i < RARRAY_LEN(args); ++i) {
-    VALUE v = RARRAY_PTR(args)[i];
-    strcat(buffer, StringValuePtr(v));
-    strcat(buffer, "_");
-  }
-  buffer[strlen(buffer) - 1] = 0;
-  return rb_str_new2(buffer);
-
+VALUE proc_spec_rb_proc_new_function(VALUE args) {
+  return rb_funcall(args, rb_intern("inspect"), 0);
 }
 
-VALUE proc_spec_underline_concat_proc(VALUE self) {
-  return rb_proc_new(proc_spec_concat_func, Qnil);
+VALUE proc_spec_rb_proc_new(VALUE self) {
+  return rb_proc_new(proc_spec_rb_proc_new_function, Qnil);
 }
 #endif
 
+/* This helper is not strictly necessary but reflects the code in wxRuby that
+ * originally exposed issues with this Proc.new behavior.
+ */
 VALUE proc_spec_rb_Proc_new_helper(void) {
   return rb_funcall(rb_cProc, rb_intern("new"), 0);
 }
 
-VALUE proc_spec_rb_Proc_new(VALUE self, VALUE do_call) {
-  if(RTEST(do_call)) {
-    rb_funcall(self, rb_intern("nil?"), 0);
+VALUE proc_spec_rb_Proc_new(VALUE self, VALUE scenario) {
+  switch(FIX2INT(scenario)) {
+    case 0:
+      return proc_spec_rb_Proc_new_helper();
+    case 1:
+      rb_funcall(self, rb_intern("call_nothing"), 0);
+      return proc_spec_rb_Proc_new_helper();
+    case 2:
+      return rb_funcall(self, rb_intern("call_Proc_new"), 0);
+    case 3:
+      return rb_funcall(self, rb_intern("call_rb_Proc_new"), 0);
+    case 4:
+      return rb_funcall(self, rb_intern("call_rb_Proc_new_with_block"), 0);
+    case 5:
+      rb_funcall(self, rb_intern("call_rb_Proc_new_with_block"), 0);
+      return proc_spec_rb_Proc_new_helper();
+    case 6:
+      return rb_funcall(self, rb_intern("call_block_given?"), 0);
+    default:
+      rb_raise(rb_eException, "invalid scenario");
   }
 
-  return proc_spec_rb_Proc_new_helper();
+  return Qnil;
 }
 
 void Init_proc_spec() {
@@ -43,7 +54,7 @@ void Init_proc_spec() {
   cls = rb_define_class("CApiProcSpecs", rb_cObject);
 
 #ifdef HAVE_RB_PROC_NEW
-  rb_define_method(cls, "underline_concat_proc", proc_spec_underline_concat_proc, 0);
+  rb_define_method(cls, "rb_proc_new", proc_spec_rb_proc_new, 0);
 #endif
 
   rb_define_method(cls, "rb_Proc_new", proc_spec_rb_Proc_new, 1);
diff --git a/spec/ruby/optional/capi/fixtures/proc.rb b/spec/ruby/optional/capi/fixtures/proc.rb
new file mode 100644
index 0000000000..fbe37312da
--- /dev/null
+++ b/spec/ruby/optional/capi/fixtures/proc.rb
@@ -0,0 +1,20 @@
+class CApiProcSpecs
+  def call_nothing
+  end
+
+  def call_Proc_new
+    Proc.new
+  end
+
+  def call_block_given?
+    block_given?
+  end
+
+  def call_rb_Proc_new
+    rb_Proc_new(0)
+  end
+
+  def call_rb_Proc_new_with_block
+    rb_Proc_new(0) { :calling_with_block }
+  end
+end
diff --git a/spec/ruby/optional/capi/hash_spec.rb b/spec/ruby/optional/capi/hash_spec.rb
index 610da0a407..6ba2279f40 100644
--- a/spec/ruby/optional/capi/hash_spec.rb
+++ b/spec/ruby/optional/capi/hash_spec.rb
@@ -45,6 +45,10 @@
     it "returns a new hash" do
       @s.rb_hash_new.should == {}
     end
+
+    it "creates a hash with no default proc" do
+      @s.rb_hash_new {}.default_proc.should be_nil
+    end
   end
 
   describe "rb_hash_aref" do
diff --git a/spec/ruby/optional/capi/proc_spec.rb b/spec/ruby/optional/capi/proc_spec.rb
index c107050170..57ef76fb21 100644
--- a/spec/ruby/optional/capi/proc_spec.rb
+++ b/spec/ruby/optional/capi/proc_spec.rb
@@ -1,39 +1,112 @@
 require File.expand_path('../spec_helper', __FILE__)
+require File.expand_path('../fixtures/proc', __FILE__)
 
 load_extension("proc")
 
-describe "CApiProc" do
+describe "C-API Proc function" do
   before :each do
     @p = CApiProcSpecs.new
+    @prc = @p.rb_proc_new
   end
 
-  it "rb_proc_new should return a new valid Proc" do
-    my_proc = @p.underline_concat_proc()
-    my_proc.kind_of?(Proc).should == true
-    my_proc.call('foo', 'bar').should == 'foo_bar'
-    my_proc['foo', 'bar'].should == 'foo_bar'
-  end
+  describe "rb_proc_new" do
+    it "returns a new valid Proc" do
+      @prc.kind_of?(Proc).should == true
+    end
 
-  it "rb_proc_new returned proc should have arity -1" do
-    my_proc = @p.underline_concat_proc()
-    my_proc.arity.should == -1
+    ruby_version_is "" ... "1.8.7" do
+      it "calls the C function wrapped by the Proc instance when sent #call" do
+        @prc.call(:foo_bar).should == "[:foo_bar]"
+        @prc.call([:foo, :bar]).should == "[:foo, :bar]"
+      end
+
+      it "calls the C function wrapped by the Proc instance when sent #[]" do
+        @prc[:foo_bar].should == "[:foo_bar]"
+        @prc[[:foo, :bar]].should == "[:foo, :bar]"
+      end
+    end
+
+    ruby_version_is "1.8.7" ... "1.9" do
+      it "calls the C function wrapped by the Proc instance when sent #call" do
+        @prc.call(:foo_bar).should == "[:foo_bar]"
+        @prc.call([:foo, :bar]).should == "[[:foo, :bar]]"
+      end
+
+      it "calls the C function wrapped by the Proc instance when sent #[]" do
+        @prc[:foo_bar].should == "[:foo_bar]"
+        @prc[[:foo, :bar]].should == "[[:foo, :bar]]"
+      end
+    end
+
+    ruby_version_is "1.9" do
+      it "calls the C function wrapped by the Proc instance when sent #call" do
+        @prc.call(:foo_bar).should == ":foo_bar"
+        @prc.call([:foo, :bar]).should == "[:foo, :bar]"
+      end
+
+      it "calls the C function wrapped by the Proc instance when sent #[]" do
+        @prc[:foo_bar].should == ":foo_bar"
+        @prc[[:foo, :bar]].should == "[:foo, :bar]"
+      end
+    end
+
+    it "returns a Proc instance with #aricy == -1" do
+      @prc.arity.should == -1
+    end
   end
 end
 
-describe "C-API" do
+describe "C-API when calling Proc.new from a C function" do
   before :each do
     @p = CApiProcSpecs.new
   end
 
-  describe "when calling Proc.new from the C-API" do
-    it "returns the proc passed to the Ruby method calling into C" do
-      prc = @p.rb_Proc_new(false) { :called }
-      prc.call.should == :called
-    end
+  # In the scenarios below: X -> Y means execution context X called to Y.
+  # For example: Ruby -> C means a Ruby code called a C function.
+  #
+  # X -> Y <- X -> Z means exection context X called Y which returned to X,
+  # then X called Z.
+  # For example: C -> Ruby <- C -> Ruby means a C function called into Ruby
+  # code which returned to C, then C called into Ruby code again.
 
-    it "returns the proc passed to the Ruby method when multiple rb_funcall's are issued" do
-      prc = @p.rb_Proc_new(true) { :called }
-      prc.call.should == :called
-    end
+  #   Ruby -> C -> rb_funcall(Proc.new)
+  it "returns the Proc passed by the Ruby code calling the C function" do
+    prc = @p.rb_Proc_new(0) { :called }
+    prc.call.should == :called
+  end
+
+  #   Ruby -> C -> Ruby <- C -> rb_funcall(Proc.new)
+  it "returns the Proc passed to the Ruby method when the C function calls other Ruby methods before calling Proc.new" do
+    prc = @p.rb_Proc_new(1) { :called }
+    prc.call.should == :called
+  end
+
+  # Ruby -> C -> Ruby -> Proc.new
+  it "raises an ArgumentError when the C function calls a Ruby method that calls Proc.new" do
+    def @p.Proc_new() Proc.new end
+    lambda { @p.rb_Proc_new(2) { :called } }.should raise_error(ArgumentError)
+  end
+
+  # Ruby -> C -> Ruby -> C -> rb_funcall(Proc.new)
+  it "raises an ArgumentError when the C function calls a Ruby method and that method calls a C function that calls Proc.new" do
+    def @p.redispatch() rb_Proc_new(0) end
+    lambda { @p.rb_Proc_new(3) { :called } }.should raise_error(ArgumentError)
+  end
+
+  # Ruby -> C -> Ruby -> C (with new block) -> rb_funcall(Proc.new)
+  it "returns the most recent Proc passed when the Ruby method called the C function" do
+    prc = @p.rb_Proc_new(4) { :called }
+    prc.call.should == :calling_with_block
+  end
+
+  # Ruby -> C -> Ruby -> C (with new block) <- Ruby <- C -> # rb_funcall(Proc.new)
+  it "returns the Proc passed from the original Ruby call to the C function" do
+    prc = @p.rb_Proc_new(5) { :called }
+    prc.call.should == :called
+  end
+
+  # Ruby -> C -> Ruby -> block_given?
+  it "returns false from block_given? in a Ruby method called by the C function" do
+    @p.rb_Proc_new(6).should be_false
   end
 end