diff --git a/src/jrd/optimizer/Retrieval.cpp b/src/jrd/optimizer/Retrieval.cpp
index 5ecacf746e..ef6b11c6da 100644
--- a/src/jrd/optimizer/Retrieval.cpp
+++ b/src/jrd/optimizer/Retrieval.cpp
@@ -1414,17 +1414,37 @@ InversionCandidate* Retrieval::makeInversion(InversionCandidateList& inversions)
 
 	for (auto inversion : inversions)
 	{
-		const auto indexScratch = inversion->scratch;
-
-		// If the explicit plan doesn't mention this index, fake it as used
-		// thus excluding it from the cost-based algorithm. Otherwise,
-		// given this index is suitable for navigation, also mark it as used.
-
-		if ((indexScratch &&
-			(indexScratch->index->idx_runtime_flags & idx_plan_dont_use)) ||
-			(!customPlan && inversion == navigationCandidate))
+		if (const auto indexScratch = inversion->scratch)
 		{
-			inversion->used = true;
+			const auto idx = indexScratch->index;
+
+			// If the explicit plan doesn't mention this index, fake it as used
+			// thus excluding it from the cost-based algorithm. Otherwise,
+			// given this index is suitable for navigation, also mark it as used.
+
+			if (((idx->idx_runtime_flags & idx_plan_dont_use)) ||
+				(!customPlan && inversion == navigationCandidate))
+			{
+				inversion->used = true;
+			}
+
+			// If the index is conditional and its condition is also present in
+			// some other inversion as a boolean (it represents the OR operation),
+			// fake these other inversions as used, so that the full index scan would
+			// be preferred to multiple range scans. The cost-based algorithm below
+			// cannot handle it currently.
+
+			if (idx->idx_flags & idx_condition)
+			{
+				for (auto otherInversion : inversions)
+				{
+					if (otherInversion->boolean &&
+						idx->idx_condition->sameAs(otherInversion->boolean, true))
+					{
+						otherInversion->used = true;
+					}
+				}
+			}
 		}
 	}
 
@@ -1460,11 +1480,9 @@ InversionCandidate* Retrieval::makeInversion(InversionCandidateList& inversions)
 					if (!invCandidate)
 						invCandidate = FB_NEW_POOL(getPool()) InversionCandidate(getPool());
 
-					if (!currentInv->inversion && currentInv->scratch)
-						invCandidate->inversion = makeIndexScanNode(currentInv->scratch);
-					else
-						invCandidate->inversion = currentInv->inversion;
-
+					const auto inversionNode = (!currentInv->inversion && currentInv->scratch) ?
+						makeIndexScanNode(currentInv->scratch) : currentInv->inversion;
+					invCandidate->inversion = inversionNode;
 					invCandidate->dbkeyRanges.assign(currentInv->dbkeyRanges);
 					invCandidate->unique = currentInv->unique;
 					invCandidate->selectivity = currentInv->selectivity;
@@ -1653,12 +1671,9 @@ InversionCandidate* Retrieval::makeInversion(InversionCandidateList& inversions)
 				if (!invCandidate)
 				{
 					invCandidate = FB_NEW_POOL(getPool()) InversionCandidate(getPool());
-					if (!bestCandidate->inversion && bestCandidate->scratch) {
-						invCandidate->inversion = makeIndexScanNode(bestCandidate->scratch);
-					}
-					else {
-						invCandidate->inversion = bestCandidate->inversion;
-					}
+					const auto inversionNode = (!bestCandidate->inversion && bestCandidate->scratch) ?
+						makeIndexScanNode(bestCandidate->scratch) : bestCandidate->inversion;
+					invCandidate->inversion = inversionNode;
 					invCandidate->dbkeyRanges.assign(bestCandidate->dbkeyRanges);
 					invCandidate->unique = bestCandidate->unique;
 					invCandidate->selectivity = bestCandidate->selectivity;
@@ -1685,17 +1700,10 @@ InversionCandidate* Retrieval::makeInversion(InversionCandidateList& inversions)
 				}
 				else if (!bestCandidate->condition)
 				{
-					if (!bestCandidate->inversion && bestCandidate->scratch)
-					{
-						invCandidate->inversion = composeInversion(invCandidate->inversion,
-							makeIndexScanNode(bestCandidate->scratch), InversionNode::TYPE_AND);
-					}
-					else
-					{
-						invCandidate->inversion = composeInversion(invCandidate->inversion,
-							bestCandidate->inversion, InversionNode::TYPE_AND);
-					}
-
+					const auto inversionNode = (!bestCandidate->inversion && bestCandidate->scratch) ?
+						makeIndexScanNode(bestCandidate->scratch) : bestCandidate->inversion;
+					invCandidate->inversion = composeInversion(invCandidate->inversion,
+						inversionNode, InversionNode::TYPE_AND);
 					invCandidate->dbkeyRanges.join(bestCandidate->dbkeyRanges);
 					invCandidate->unique = (invCandidate->unique || bestCandidate->unique);
 					invCandidate->selectivity = totalSelectivity;
@@ -1770,6 +1778,16 @@ bool Retrieval::matchBoolean(IndexScratch* indexScratch,
 	if (boolean->nodFlags & ExprNode::FLAG_DEOPTIMIZE)
 		return false;
 
+	const auto idx = indexScratch->index;
+
+	if (idx->idx_flags & idx_condition)
+	{
+		// If index condition matches the boolean, this should not be
+		// considered a match. Full index scan will be used instead.
+		if (idx->idx_condition->sameAs(boolean, true))
+			return false;
+	}
+
 	const auto cmpNode = nodeAs<ComparativeBoolNode>(boolean);
 	const auto missingNode = nodeAs<MissingBoolNode>(boolean);
 	const auto listNode = nodeAs<InListBoolNode>(boolean);
@@ -1804,16 +1822,6 @@ bool Retrieval::matchBoolean(IndexScratch* indexScratch,
 	ValueExprNode* value2 = (cmpNode && cmpNode->blrOp == blr_between) ?
 		cmpNode->arg3 : nullptr;
 
-	const auto idx = indexScratch->index;
-
-	if (idx->idx_flags & idx_condition)
-	{
-		// If index condition matches the boolean, this should not be
-		// considered a match. Full index scan will be used instead.
-		if (idx->idx_condition->sameAs(boolean, true))
-			return false;
-	}
-
 	if (idx->idx_flags & idx_expression)
 	{
 		// see if one side or the other is matchable to the index expression