diff --git a/IPhreeqc.vcproj b/IPhreeqc.vcproj
index 9454f75c..bf680e9b 100644
--- a/IPhreeqc.vcproj
+++ b/IPhreeqc.vcproj
@@ -44,6 +44,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="2"
 				InlineFunctionExpansion="1"
 				AdditionalIncludeDirectories="src;src/phreeqcpp;src/phreeqcpp/phreeqc"
@@ -187,6 +188,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="0"
 				AdditionalIncludeDirectories="src;src/phreeqcpp;src/phreeqcpp/phreeqc"
 				PreprocessorDefinitions="_DEBUG;WIN32;_LIB"
@@ -332,6 +334,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="2"
 				InlineFunctionExpansion="1"
 				AdditionalIncludeDirectories="src;src/phreeqcpp;src/phreeqcpp/phreeqc"
@@ -495,6 +498,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="0"
 				AdditionalIncludeDirectories="src;src/phreeqcpp;src/phreeqcpp/phreeqc"
 				PreprocessorDefinitions="_DEBUG;WIN32;_LIB"
diff --git a/unit/unit.vcproj b/unit/unit.vcproj
index 0c4333a6..afc7b8db 100644
--- a/unit/unit.vcproj
+++ b/unit/unit.vcproj
@@ -46,6 +46,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="0"
 				AdditionalIncludeDirectories="&quot;$(DEV_CPPUNIT_1.10)/include&quot;;../src;../src/phreeqcpp;../src/phreeqcpp/phreeqc"
 				PreprocessorDefinitions="CPPUNIT;WIN32;_DEBUG;_CONSOLE"
@@ -207,6 +208,7 @@
 			/>
 			<Tool
 				Name="VCCLCompilerTool"
+				AdditionalOptions="/MP"
 				Optimization="2"
 				InlineFunctionExpansion="1"
 				AdditionalIncludeDirectories="&quot;$(DEV_CPPUNIT_1.10)/include&quot;;../src;../src/phreeqcpp;../src/phreeqcpp/phreeqc"