diff --git a/src/jrd/optimizer/Optimizer.cpp b/src/jrd/optimizer/Optimizer.cpp
index af0431b486..ebf077dc9d 100644
--- a/src/jrd/optimizer/Optimizer.cpp
+++ b/src/jrd/optimizer/Optimizer.cpp
@@ -174,6 +174,7 @@ namespace
 			// Save states of the underlying streams and restore them afterwards
 
 			StreamStateHolder stateHolder(csb, m_streams);
+			stateHolder.deactivate();
 
 			// Generate record source objects
 
@@ -569,7 +570,6 @@ Optimizer::Optimizer(thread_db* aTdbb, CompilerScratch* aCsb, RseNode* aRse, boo
 	  compileStreams(getPool()),
 	  bedStreams(getPool()),
 	  keyStreams(getPool()),
-	  subStreams(getPool()),
 	  outerStreams(getPool()),
 	  conjuncts(getPool())
 {
@@ -814,7 +814,7 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 	// Go through the record selection expression generating
 	// record source blocks for all streams
 
-	RiverList rivers;
+	RiverList rivers, dependentRivers;
 
 	bool innerSubStream = false;
 	for (auto node : rse->rse_relations)
@@ -840,11 +840,13 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 			StreamList localStreams;
 			rsb->findUsedStreams(localStreams);
 
+			bool computable = false;
+
 			// AB: Save all outer-part streams
 			if (isInnerJoin() || (isLeftJoin() && !innerSubStream))
 			{
-				subStreams.join(localStreams);
-				outerStreams.join(localStreams);
+				if (node->computable(csb, INVALID_STREAM, false))
+					computable = true;
 
 				// Apply local booleans, if any. Note that it's done
 				// only for inner joins and outer streams of left joins.
@@ -854,7 +856,16 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 
 			const auto river = FB_NEW_POOL(getPool()) River(csb, rsb, node, localStreams);
 			river->deactivate(csb);
-			rivers.add(river);
+
+			if (computable)
+			{
+				outerStreams.join(localStreams);
+				rivers.add(river);
+			}
+			else
+			{
+				dependentRivers.add(river);
+			}
 		}
 		else
 		{
@@ -883,9 +894,9 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 	else
 		rse->rse_aggregate = aggregate = nullptr;
 
-	// AB: Mark the previous used streams (sub-RseNode's) as active
-	for (const auto subStream : subStreams)
-		csb->csb_rpt[subStream].activate();
+	// Activate the priorly used rivers
+	for (const auto river : rivers)
+		river->activate(csb);
 
 	bool sortCanBeUsed = true;
 	SortNode* const orgSortNode = sort;
@@ -904,7 +915,10 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 
 	// Outer joins are processed their own way
 	if (!isInnerJoin())
+	{
+		rivers.join(dependentRivers);
 		rsb = generateOuterJoin(rivers, &sort);
+	}
 	else
 	{
 		// AB: If previous rsb's are already on the stack we can't use
@@ -971,13 +985,18 @@ RecordSource* Optimizer::compile(BoolExprNodeStack* parentStack)
 			}
 		}
 
-		// attempt to form joins in decreasing order of desirability
+		// Attempt to form joins in decreasing order of desirability
 		generateInnerJoin(joinStreams, rivers, &sort, rse->rse_plan);
 
+		// Re-activate remaining rivers to be hashable/mergeable
+		for (const auto river : rivers)
+			river->activate(csb);
+
 		// If there are multiple rivers, try some hashing or sort/merging
 		while (generateEquiJoin(rivers))
 			;
 
+		rivers.join(dependentRivers);
 		rsb = CrossJoin(csb, rivers).getRecordSource();
 
 		// Pick up any residual boolean that may have fallen thru the cracks
@@ -2263,6 +2282,9 @@ bool Optimizer::generateEquiJoin(RiverList& orgRivers)
 		if (iter & CONJUNCT_USED)
 			continue;
 
+		if (!iter->computable(csb, INVALID_STREAM, false))
+			continue;
+
 		NestConst<ValueExprNode> node1;
 		NestConst<ValueExprNode> node2;
 
diff --git a/src/jrd/optimizer/Optimizer.h b/src/jrd/optimizer/Optimizer.h
index ef9baa0f1a..3cc9b1de51 100644
--- a/src/jrd/optimizer/Optimizer.h
+++ b/src/jrd/optimizer/Optimizer.h
@@ -548,7 +548,7 @@ private:
 	unsigned baseParentConjuncts = 0;		// number of conjuncts in our rse + distributed with parent, next are parent
 	unsigned baseMissingConjuncts = 0;		// number of conjuncts in our and parent rse, but without missing
 
-	StreamList compileStreams, bedStreams, keyStreams, subStreams, outerStreams;
+	StreamList compileStreams, bedStreams, keyStreams, outerStreams;
 	ConjunctList conjuncts;
 };