diff --git a/Source/levels/gendung.cpp b/Source/levels/gendung.cpp
index 4946ea30a..036c86643 100644
--- a/Source/levels/gendung.cpp
+++ b/Source/levels/gendung.cpp
@@ -351,6 +351,13 @@ void InitGlobals()
 
 } // namespace
 
+#ifdef BUILD_TESTING
+std::optional<Size> GetSizeForThemeRoom()
+{
+	return GetSizeForThemeRoom(0, { 0, 0 }, 5, 10);
+}
+#endif
+
 dungeon_type GetLevelType(int level)
 {
 	if (level == 0)
diff --git a/Source/levels/gendung.h b/Source/levels/gendung.h
index 85cca8e18..e2253c286 100644
--- a/Source/levels/gendung.h
+++ b/Source/levels/gendung.h
@@ -215,6 +215,10 @@ extern char dSpecial[MAXDUNX][MAXDUNY];
 extern int themeCount;
 extern THEME_LOC themeLoc[MAXTHEMES];
 
+#ifdef BUILD_TESTING
+std::optional<Size> GetSizeForThemeRoom();
+#endif
+
 dungeon_type GetLevelType(int level);
 void CreateDungeon(uint32_t rseed, lvl_entry entry);
 
diff --git a/test/drlg_common_test.cpp b/test/drlg_common_test.cpp
index 171dc87a6..e564c22ba 100644
--- a/test/drlg_common_test.cpp
+++ b/test/drlg_common_test.cpp
@@ -4,6 +4,7 @@
 #include <array>
 
 #include "engine/points_in_rectangle_range.hpp"
+#include "levels/gendung.h"
 
 namespace devilution {
 
@@ -70,4 +71,38 @@ TEST(DrlgTest, RectangleRangeIterator)
 	EXPECT_EQ(region[2][2], 9) << "Reverse iterators are required";
 }
 
+TEST(DrlgTest, ThemeRoomSize)
+{
+	memset(dungeon, 0, sizeof(dungeon));
+
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(8, 8)) << "All floor theme area should be 8x8";
+
+	dungeon[9][9] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(7, 7)) << "Corners shrink the chosen dimensions";
+	dungeon[9][5] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(7, 3)) << "Minimum dimensions are determined by corners outside the min area";
+	dungeon[9][4] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(7, 8)) << "Walls below the min size let larger opposing dimensions get picked";
+	dungeon[9][5] = 0;
+	dungeon[9][4] = 0;
+	dungeon[9][9] = 0;
+
+	// Time for some unusual cases
+	dungeon[7][2] = 1;
+	dungeon[5][9] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(5, 7)) << "Search space terminates at width 8 due to the wall being in the first three rows";
+
+	dungeon[6][4] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(4, 7)) << "Smallest width now defined by row 5, height still extends due to minSize";
+	dungeon[6][4] = 0;
+
+	dungeon[5][9] = 0;
+	dungeon[7][2] = 0;
+
+	dungeon[7][0] = 1;
+	dungeon[6][6] = 1;
+	dungeon[8][5] = 1;
+	EXPECT_EQ(GetSizeForThemeRoom(), Size(4, 4)) << "Search is terminated by the 0 width row 7, inset corner gives a larger height than otherwise expected";
+}
+
 } // namespace devilution