2 files changed, 3 insertions, 3 deletions
diff --git a/spec/ruby/core/argf/shared/getc.rb b/spec/ruby/core/argf/shared/getc.rb
index 8be39c60b6..d63372d9d7 100644
--- a/spec/ruby/core/argf/shared/getc.rb
+++ b/spec/ruby/core/argf/shared/getc.rb
@@ -9,7 +9,7 @@ describe :argf_getc, shared: true do
 
   it "reads each char of files" do
     argf [@file1, @file2] do
-      chars = ""
+      chars = +""
       @chars.size.times { chars << @argf.send(@method) }
       chars.should == @chars
     end
diff --git a/spec/ruby/core/argf/shared/read.rb b/spec/ruby/core/argf/shared/read.rb
index fe903983c0..e76d022139 100644
--- a/spec/ruby/core/argf/shared/read.rb
+++ b/spec/ruby/core/argf/shared/read.rb
@@ -15,7 +15,7 @@ describe :argf_read, shared: true do
 
   it "treats second argument as an output buffer" do
     argf [@file1_name] do
-      buffer = ""
+      buffer = +""
       @argf.send(@method, @file1.size, buffer)
       buffer.should == @file1
     end
@@ -23,7 +23,7 @@ describe :argf_read, shared: true do
 
   it "clears output buffer before appending to it" do
     argf [@file1_name] do
-      buffer = "to be cleared"
+      buffer = +"to be cleared"
       @argf.send(@method, @file1.size, buffer)
       buffer.should == @file1
     end