diff --git a/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/Builder.java b/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/Builder.java
index 3f6b3818677..55f4995f5c3 100644
--- a/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/Builder.java
+++ b/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/Builder.java
@@ -2522,7 +2522,13 @@ public class Builder extends HoldsOptions implements IBuilder, IMatchKeyProvider
 	 * The function never returns number smaller than 1.
 	 */
 	public int getOptimalParallelJobNum() {
-		return Runtime.getRuntime().availableProcessors();
+		// Bug 398426: On my Mac running parallel builds at full tilt hangs the desktop.
+		// Need to pull it back one.
+		int j = Runtime.getRuntime().availableProcessors();
+		if (j > 1 && Platform.getOS().equals(Platform.OS_MACOSX))
+			return j - 1;
+		else
+			return j;
 	}
 	
 	/**
diff --git a/build/org.eclipse.cdt.managedbuilder.ui/src/org/eclipse/cdt/managedbuilder/internal/ui/Messages.properties b/build/org.eclipse.cdt.managedbuilder.ui/src/org/eclipse/cdt/managedbuilder/internal/ui/Messages.properties
index 59bc380dca0..ac4acf5dce1 100644
--- a/build/org.eclipse.cdt.managedbuilder.ui/src/org/eclipse/cdt/managedbuilder/internal/ui/Messages.properties
+++ b/build/org.eclipse.cdt.managedbuilder.ui/src/org/eclipse/cdt/managedbuilder/internal/ui/Messages.properties
@@ -32,7 +32,7 @@ BuilderSettingsTab_8=&Expand Env. Variable Refs in Makefiles
 BuilderSettingsTab_9=Build settings
 BuilderSettingsTab_10=Stop on first build error
 BuilderSettingsTab_EnableParallelBuild=Enable parallel build
-BuilderSettingsTab_UseOptimalJobs=Use number of processors ({0})
+BuilderSettingsTab_UseOptimalJobs=Use optimal jobs ({0})
 BuilderSettingsTab_UseParallelJobs=Use parallel jobs: 
 BuilderSettingsTab_UseUnlimitedJobs=Use unlimited jobs
 BuilderSettingsTab_14=Workbench Build Behavior