diff --git a/src/openrct2/management/Research.cpp b/src/openrct2/management/Research.cpp
index fefe6bf3a0..8177c9bcd8 100644
--- a/src/openrct2/management/Research.cpp
+++ b/src/openrct2/management/Research.cpp
@@ -164,17 +164,25 @@ static void ResearchNextDesign()
         it = gResearchItemsUninvented.begin();
     }
 
-    const ResearchItem researchItem = *it;
-    gResearchNextItem = researchItem;
+    gResearchNextItem = *it;
     gResearchProgress = 0;
     gResearchProgressStage = RESEARCH_STAGE_DESIGNING;
 
-    gResearchItemsUninvented.erase(it);
-    gResearchItemsInvented.push_back(researchItem);
-
     ResearchInvalidateRelatedWindows();
 }
 
+static void MarkResearchItemInvented(const ResearchItem& researchItem)
+{
+    gResearchItemsUninvented.erase(
+        std::remove(gResearchItemsUninvented.begin(), gResearchItemsUninvented.end(), researchItem),
+        gResearchItemsUninvented.end());
+
+    if (std::find(gResearchItemsInvented.begin(), gResearchItemsInvented.end(), researchItem) == gResearchItemsInvented.end())
+    {
+        gResearchItemsInvented.push_back(researchItem);
+    }
+}
+
 /**
  *
  *  rct2: 0x006848D4
@@ -346,6 +354,7 @@ void ResearchUpdate()
                 ResearchInvalidateRelatedWindows();
                 break;
             case RESEARCH_STAGE_COMPLETING_DESIGN:
+                MarkResearchItemInvented(*gResearchNextItem);
                 ResearchFinishItem(*gResearchNextItem);
                 gResearchProgress = 0;
                 gResearchProgressStage = RESEARCH_STAGE_INITIAL_RESEARCH;
diff --git a/src/openrct2/management/Research.h b/src/openrct2/management/Research.h
index a0fcdbf3f2..6f5b40d7e5 100644
--- a/src/openrct2/management/Research.h
+++ b/src/openrct2/management/Research.h
@@ -139,7 +139,6 @@ void ResearchInsertRideEntry(ObjectEntryIndex entryIndex, bool researched);
 bool ResearchInsertSceneryGroupEntry(ObjectEntryIndex entryIndex, bool researched);
 
 bool ResearchIsInvented(ObjectType objectType, ObjectEntryIndex index);
-bool ResearchSetInvented(ObjectType objectType, ObjectEntryIndex index, bool value);
 void RideTypeSetInvented(uint32_t rideType);
 void RideEntrySetInvented(ObjectEntryIndex rideEntryIndex);
 void ScenerySetInvented(const ScenerySelection& sceneryItem);