diff --git a/libursa/CMakeLists.txt b/libursa/CMakeLists.txt
index 9d25f61..b4988c2 100644
--- a/libursa/CMakeLists.txt
+++ b/libursa/CMakeLists.txt
@@ -50,6 +50,8 @@ add_library(
     QueryParser.h
     QueryResult.cpp
     QueryResult.h
+    QueryOptimizer.cpp
+    QueryOptimizer.h
     RawFile.cpp
     RawFile.h
     Responses.cpp
diff --git a/libursa/OnDiskDataset.cpp b/libursa/OnDiskDataset.cpp
index 80e3210..fe6fc44 100644
--- a/libursa/OnDiskDataset.cpp
+++ b/libursa/OnDiskDataset.cpp
@@ -8,6 +8,7 @@
 #include "DatabaseName.h"
 #include "Json.h"
 #include "Query.h"
+#include "QueryOptimizer.h"
 #include "spdlog/fmt/ostr.h"
 #include "spdlog/spdlog.h"
 
@@ -91,7 +92,8 @@ void OnDiskDataset::execute(const Query &query, ResultWriter *out,
     for (const auto &ndx : get_indexes()) {
         types_to_query.emplace(ndx.index_type());
     }
-    const Query plan = query.plan(types_to_query);
+    Query plan = query.plan(types_to_query);
+    plan = q_optimize(std::move(plan));
     spdlog::debug("PLAN: {}", plan);
 
     QueryResult result = this->query(plan, counters);
diff --git a/libursa/Query.cpp b/libursa/Query.cpp
index 262df7d..33443a8 100644
--- a/libursa/Query.cpp
+++ b/libursa/Query.cpp
@@ -18,7 +18,14 @@ const std::vector<Query> &Query::as_queries() const {
         type != QueryType::MIN_OF) {
         throw std::runtime_error("This query doesn\'t contain subqueries.");
     }
+    return queries;
+}
 
+std::vector<Query> &Query::as_queries() {
+    if (type != QueryType::AND && type != QueryType::OR &&
+        type != QueryType::MIN_OF) {
+        throw std::runtime_error("This query doesn\'t contain subqueries.");
+    }
     return queries;
 }
 
diff --git a/libursa/Query.h b/libursa/Query.h
index ecc96c0..7149a80 100644
--- a/libursa/Query.h
+++ b/libursa/Query.h
@@ -22,8 +22,8 @@ class PrimitiveQuery {
     PrimitiveQuery(IndexType itype, TriGram trigram)
         : itype(itype), trigram(trigram) {}
 
-    const IndexType itype;
-    const TriGram trigram;
+    IndexType itype;
+    TriGram trigram;
 
     // We want to use PrimitiveQuery in STL containers, and this means they
     // must be comparable using <. Specific order doesn't matter.
@@ -51,6 +51,7 @@ class Query {
     Query &operator=(Query &&) = default;
 
     const std::vector<Query> &as_queries() const;
+    std::vector<Query> &as_queries();
     const QString &as_value() const;
     uint32_t as_count() const;
     std::string as_string_repr() const;
diff --git a/libursa/QueryOptimizer.cpp b/libursa/QueryOptimizer.cpp
new file mode 100644
index 0000000..f8198ce
--- /dev/null
+++ b/libursa/QueryOptimizer.cpp
@@ -0,0 +1,31 @@
+#include "QueryOptimizer.h"
+
+#include <vector>
+
+// Run the optimization pases on subqueries.
+// After this step, every subquery should be maximally optimized,
+// So I believe there's no need to run this in a loop.
+Query simplify_subqueries(Query &&q) {
+    // q_optimize ensures QueryType is not PRIMITIVE already
+    std::vector<Query> newqueries;
+    for (auto &&query : q.as_queries()) {
+        newqueries.emplace_back(q_optimize(std::move(query)));
+    }
+    if (q.get_type() == QueryType::MIN_OF) {
+        return q_min_of(q.as_count(), std::move(newqueries));
+    }
+    return std::move(Query(q.get_type(), std::move(newqueries)));
+}
+
+Query q_optimize(Query &&q) {
+    if (q.get_type() == QueryType::PRIMITIVE) {
+        // Nothing to improve here.
+        return std::move(q);
+    }
+
+    q = simplify_subqueries(std::move(q));
+
+    // Optimization passes will be added here later.
+
+    return std::move(q);
+}
diff --git a/libursa/QueryOptimizer.h b/libursa/QueryOptimizer.h
new file mode 100644
index 0000000..2d267a2
--- /dev/null
+++ b/libursa/QueryOptimizer.h
@@ -0,0 +1,8 @@
+#pragma once
+
+#include "Query.h"
+
+// Optimizes a query, and returns the optimized version.
+// Optimizations try to simplify the expression in various ways to make the
+// execution faster - for example by enabling short-circuiting in some places.
+Query q_optimize(Query &&query);
diff --git a/libursa/Version.h.in b/libursa/Version.h.in
index 73203c2..dbec52a 100644
--- a/libursa/Version.h.in
+++ b/libursa/Version.h.in
@@ -8,5 +8,6 @@ constexpr std::string_view ursadb_format_version = "1.5.0";
 
 // Project version.
 // Consider updating the version tag when doing PRs.
-constexpr std::string_view ursadb_version_string =
-    "@PROJECT_VERSION@+debuglogs";
+// clang-format off
+constexpr std::string_view ursadb_version_string = "@PROJECT_VERSION@+opt0";
+// clang-format on