diff --git a/lib/cocoapods-core/podfile/dsl.rb b/lib/cocoapods-core/podfile/dsl.rb
index 5bdfe4ae4..df732ab0a 100644
--- a/lib/cocoapods-core/podfile/dsl.rb
+++ b/lib/cocoapods-core/podfile/dsl.rb
@@ -292,6 +292,19 @@ def ensure_bundler!(version = nil)
       #
       #     pod 'JSONKit', :podspec => 'https://example.com/JSONKit.podspec'
       #
+      # ### Use a previously defined external source.
+      #
+      # If a dependency was already defined using an external source, reuse that definition:
+      #
+      #     target 'TargetA' do
+      #       # define an external source for `JSONKit`
+      #       pod 'JSONKit', :podspec => 'https://example.com/JSONKit.podspec'
+      #     end
+      #
+      #     target 'TargetB' do
+      #       # reuse the previous external source for `JSONKit`
+      #       pod 'JSONKit'
+      #     end
       #
       # @note       This method allow a nil name and the raises to be more
       #             informative.
@@ -303,6 +316,18 @@ def pod(name = nil, *requirements)
           raise StandardError, 'A dependency requires a name.'
         end
 
+        if requirements.empty? || requirements.last.is_a?(Hash)
+          theoretical_dependency = Dependency.new(name, requirements.last)
+          if theoretical_dependency.external_source.nil?
+            previously_defined_dependency = dependencies.find do |dependency|
+              dependency.root_name == theoretical_dependency.root_name && dependency.external_source
+            end
+            if previously_defined_dependency
+              requirements = [previously_defined_dependency.external_source]
+            end
+          end
+        end
+
         current_target_definition.store_pod(name, *requirements)
       end
 
diff --git a/lib/cocoapods-core/podfile/target_definition.rb b/lib/cocoapods-core/podfile/target_definition.rb
index 9d0307322..9a9e2fc8e 100644
--- a/lib/cocoapods-core/podfile/target_definition.rb
+++ b/lib/cocoapods-core/podfile/target_definition.rb
@@ -174,7 +174,7 @@ def abstract=(abstract)
       # @return [String] the inheritance mode for this target definition.
       #
       def inheritance
-        get_hash_value('inheritance', 'complete')
+        get_hash_value('inheritance') || 'complete'
       end
 
       # Sets the inheritance mode for this target definition.
@@ -907,7 +907,7 @@ def get_hash_value(key, base_value = nil)
         unless HASH_KEYS.include?(key)
           raise StandardError, "Unsupported hash key `#{key}`"
         end
-        internal_hash[key] = base_value if internal_hash[key].nil?
+        internal_hash[key] ||= base_value unless base_value.nil?
         internal_hash[key]
       end
 
diff --git a/spec/podfile/dsl_spec.rb b/spec/podfile/dsl_spec.rb
index 806aba659..427ffec5e 100644
--- a/spec/podfile/dsl_spec.rb
+++ b/spec/podfile/dsl_spec.rb
@@ -411,6 +411,24 @@ module Pod
         target.dependencies.sort_by(&:name).should == expected_dependencies
       end
 
+      it 'implicitly reuses an external source' do
+        podfile = Podfile.new do
+          target 'A' do
+            pod 'RestKit', :git => 'https://github.com/RestKit/RestKit.git'
+          end
+
+          target 'B' do
+            pod 'RestKit'
+          end
+        end
+
+        expected_dependencies = [
+          Dependency.new('RestKit', :git => 'https://github.com/RestKit/RestKit.git'),
+        ]
+        podfile.target_definitions['A'].dependencies.sort_by(&:name).should == expected_dependencies
+        podfile.target_definitions['B'].dependencies.sort_by(&:name).should == expected_dependencies
+      end
+
       it 'raises if no name is specified for a Pod' do
         lambda do
           Podfile.new do