diff --git a/src/tools/qt3.jam b/src/tools/qt3.jam
index 4148f9422..ba7c63928 100644
--- a/src/tools/qt3.jam
+++ b/src/tools/qt3.jam
@@ -51,19 +51,19 @@ rule init ( prefix ? )
         .initialized = true ;
         .prefix = $(prefix) ;
         
-        generators.register-standard qt3.moc : H : CPP(moc_%) : <allow>qt ;    
+        generators.register-standard qt3.moc : H : CPP(moc_%) : <allow>qt3 ;
         # Note: the OBJ target type here is fake, take a look
         # at qt4.jam/uic-h-generator for explanations that
         # apply in this case as well.
-        generators.register [ new moc-h-generator 
-            qt3.moc.cpp : MOCCABLE_CPP : OBJ : <allow>qt ] ;
+        generators.register [ new moc-h-generator-qt3 
+            qt3.moc.cpp : MOCCABLE_CPP : OBJ : <allow>qt3 ] ;
         
         # The UI type is defined in types/qt.jam,
         # and UIC_H is only used in qt.jam, but not in qt4.jam, so
         # define it here.
         type.register UIC_H : : H ;
         
-        generators.register-standard qt3.uic-h : UI : UIC_H : <allow>qt ;
+        generators.register-standard qt3.uic-h : UI : UIC_H : <allow>qt3 ;
         
         # The following generator is used to convert UI files to CPP
         # It creates UIC_H from UI, and constructs CPP from UI/UIC_H
@@ -73,7 +73,7 @@ rule init ( prefix ? )
         {
             rule __init__ ( )
             {
-                generator.__init__ qt3.uic-cpp : UI UIC_H : CPP : <allow>qt ;
+                generator.__init__ qt3.uic-cpp : UI UIC_H : CPP : <allow>qt3 ;
             }
                         
             rule run ( project name ? : properties * : sources + )
@@ -118,14 +118,14 @@ rule init ( prefix ? )
              <include>$(.prefix)/include 
              <dll-path>$(.prefix)/lib
              <library-path>$(.prefix)/lib     
-             <allow>qt
+             <allow>qt3
              ;  
         lib qt : : <name>qt-mt <threading>multi : : $(usage-requirements) ;
         lib qt : : <name>qt <threading>single : : $(usage-requirements) ;        
     }
 }
 
-class moc-h-generator : generator
+class moc-h-generator-qt3 : generator
 {
     rule __init__ ( * : * )
     {
diff --git a/src/tools/qt4.jam b/src/tools/qt4.jam
index a919a2251..72bf1d67d 100644
--- a/src/tools/qt4.jam
+++ b/src/tools/qt4.jam
@@ -74,19 +74,20 @@ rule init ( prefix )
         .prefix = $(prefix) ;
 
         # Generates cpp files from header files using "moc" tool
-        generators.register-standard qt4.moc : H : CPP(moc_%) ;
+        generators.register-standard qt4.moc : H : CPP(moc_%) : <allow>qt4 ;
         
         # The OBJ result type is a fake, 'H' will be really produces.
         # See comments on the generator calss, defined below 
         # the 'init' function.
-        generators.register [ new uic-h-generator qt4.uic-h : UI : OBJ ] ;
+        generators.register [ new uic-h-generator qt4.uic-h : UI : OBJ
+            : <allow>qt4  ] ;
         
         # The OBJ result type is a fake here too.
         generators.register [ new moc-h-generator 
-            qt4.moc.inc : MOCCABLE_CPP : OBJ ] ;
+            qt4.moc.inc : MOCCABLE_CPP : OBJ : <allow>qt4 ] ;
 
         generators.register [ new moc-inc-generator 
-            qt4.moc.inc : MOCCABLE_H : OBJ ] ;
+            qt4.moc.inc : MOCCABLE_H : OBJ : <allow>qt4 ] ;
 
         # Generates .cpp file from qrc file
         generators.register-standard qt4.rcc : QRC : CPP(qrc_%) ;
@@ -98,7 +99,12 @@ rule init ( prefix )
             local all-libraries = QtCore QtGui QtNetwork QtXml QtSql QtSvg Qt3Support QtTest QtAssistantClient QtUiTools ;
             for local l in $(all-libraries) 
             {
-                alias $(l) : $(.prefix)//$(l) ;
+                alias $(l) 
+                  : $(.prefix)//$(l) 
+                  : 
+                  : 
+                  : <allow>qt4 
+                  ;
                 explicit $(l) ;
             }
         }
@@ -109,7 +115,9 @@ rule init ( prefix )
                 <include>$(.prefix)/include 
                 <library-path>$(.prefix)/lib 
                 <dll-path>$(.prefix)/lib 
-                <threading>multi ;
+                <threading>multi 
+                <allow>qt4
+                ;
             
             local suffix ;
             if [ os.name ] = NT