diff --git a/.travis.yml b/.travis.yml
index 34333ed0..8edc2481 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,6 @@ env:
   - USE_REF=1         # Installs OpenBLAS and reference LAPACK, builds and tests nmatrix, nmatrix-lapacke
   - NO_EXTERNAL_LIB=1 # No external libraries installed, only nmatrix
 rvm:
-  - 1.9.3
   - 2.0.0-p648
   - 2.1.8
   - 2.2.4
@@ -91,19 +90,19 @@ matrix:
       env:
         - ruby_version=2.1.8 USE_OPENBLAS=1
   allow_failures:
-    # Ruby versions which got EOL
-    - rvm: 1.9.3
     # trunk
     - rvm: ruby-head
     - rvm: ruby-head-clang
-    - env: ruby_version=2.4.0-dev USE_OPENBLAS=1
-    - env: ruby_version=2.4.0-dev NO_EXTERNAL_LIB=1
-    # linux with clang
-    - os: linux
-      rvm: 2.3.0-clang
-    # For some reason this OpenBLAS configuration isn't working on travis, disable it for now.
-    - os: linux
-      env: USE_OPENBLAS=1
+    - os: osx
+      compiler: clang
+      rvm: 2.2
+      env:
+        - ruby_version=2.4.0-dev USE_OPENBLAS=1
+    - os: osx
+      compiler: clang
+      rvm: 2.2
+      env:
+        - ruby_version=2.4.0-dev NO_EXTERNAL_LIB=1
 
 notifications:
   irc: "chat.freenode.net#sciruby"
diff --git a/ext/nmatrix/data/ruby_object.h b/ext/nmatrix/data/ruby_object.h
index 6d9d21e3..c909938c 100644
--- a/ext/nmatrix/data/ruby_object.h
+++ b/ext/nmatrix/data/ruby_object.h
@@ -110,7 +110,7 @@ class RubyObject {
   inline operator VALUE() const { return rval; }
   //inline operator uint32_t() const { return NUM2ULONG(this->rval);      }
   inline operator int64_t() const { RETURN_OBJ2NUM(NUM2LONG)        }
-  inline operator uint64_t() const { RETURN_OBJ2NUM(NUM2ULONG)      }
+  //inline operator uint64_t() const { RETURN_OBJ2NUM(NUM2ULONG)      }
   inline operator double()   const { RETURN_OBJ2NUM(NUM2DBL)        }
   inline operator float()  const { RETURN_OBJ2NUM(NUM2DBL)          }
 
diff --git a/nmatrix.gemspec b/nmatrix.gemspec
index 03ac2086..e22f35dc 100644
--- a/nmatrix.gemspec
+++ b/nmatrix.gemspec
@@ -57,7 +57,6 @@ EOF
 
   gem.add_dependency 'packable', '~> 1.3', '>= 1.3.5'
   gem.add_development_dependency 'bundler', '~>1.6'
-  gem.add_development_dependency 'json', '~>2.0.1' if RUBY_VERSION >= '2.1.0'
   gem.add_development_dependency 'pry', '~>0.10'
   gem.add_development_dependency 'rake', '~>10.3'
   gem.add_development_dependency 'rake-compiler', '~>0.8'
diff --git a/travis.sh b/travis.sh
index 3bc23891..2fefe2d1 100755
--- a/travis.sh
+++ b/travis.sh
@@ -37,12 +37,12 @@ then
 
     # Install ruby
     (
-      brew install bison openssl readline libyaml
+      brew install bison openssl readline
       brew link --force openssl
       RBENV_VERSION=system
       MAKEOPTS='-j 4'
       CONFIGURE_OPTS="--disable-install-doc --with-out-ext=tk,tk/tkutil --with-opt-dir=/usr/local"
-      rbenv install $ruby_version
+      rbenv install --verbose $ruby_version
     )
 
     gem pristine --all