diff --git a/spec/System/TestGemGroupCount_spec.lua b/spec/System/TestGemGroupCount_spec.lua
new file mode 100644
index 0000000000..45ed574eaa
--- /dev/null
+++ b/spec/System/TestGemGroupCount_spec.lua
@@ -0,0 +1,73 @@
+-- Socket groups whose active skill is provided by an item or the passive tree
+-- must not count against the character's skill slot limit. Support gems never
+-- occupy a skill slot on their own, so adding one to such a group must not
+-- change whether the group is counted.
+describe("TestGemGroupCount", function()
+	before_each(function()
+		newBuild()
+		runCallback("OnFrame")
+	end)
+
+	-- Bow Shot is the default attack granted by having a bow equipped; its
+	-- granted effect carries fromItem = true in Data/Skills/other.lua.
+	local BOW_SHOT = "Metadata/Items/Gems/SkillGemPlayerDefaultBow"
+	local ICE_SHOT = "Metadata/Items/Gems/SkillGemIceShot"
+	local RAPID_ATTACKS = "Metadata/Items/Gems/SkillGemRapidAttacksSupport"
+
+	local function gem(gemId)
+		return {
+			gemId = gemId, level = 1, quality = 0, enabled = true, count = 1,
+			enableGlobal1 = true, enableGlobal2 = true,
+		}
+	end
+
+	local function addGroup(...)
+		local group = { enabled = true, gemList = { } }
+		for _, gemId in ipairs({ ... }) do
+			table.insert(group.gemList, gem(gemId))
+		end
+		table.insert(build.skillsTab.socketGroupList, group)
+		build.skillsTab:ProcessSocketGroup(group)
+		return group
+	end
+
+	local function groupCount()
+		build.skillsTab:UpdateGlobalGemCountAssignments()
+		return GlobalGemAssignments["GemGroupCount"]
+	end
+
+	it("counts a normal active skill group", function()
+		addGroup(ICE_SHOT)
+		assert.are.equals(1, groupCount())
+	end)
+
+	it("does not count the default weapon attack on its own", function()
+		addGroup(BOW_SHOT)
+		assert.are.equals(0, groupCount())
+	end)
+
+	it("does not count the default weapon attack when supported", function()
+		addGroup(BOW_SHOT, RAPID_ATTACKS)
+		assert.are.equals(0, groupCount())
+	end)
+
+	it("counts a supported normal skill exactly once", function()
+		addGroup(ICE_SHOT, RAPID_ATTACKS)
+		assert.are.equals(1, groupCount())
+	end)
+
+	-- Skills granted by an equipped item get fromItem set on the gem instance
+	-- itself (CalcSetup.lua, "activeGemInstance.fromItem = grantedSkill.sourceItem ~= nil"),
+	-- rather than on the granted effect. Both paths must survive a support gem.
+	it("does not count an item granted skill when supported", function()
+		local group = addGroup(ICE_SHOT, RAPID_ATTACKS)
+		group.gemList[1].fromItem = true
+		assert.are.equals(0, groupCount())
+	end)
+
+	it("ignores a disabled group", function()
+		local group = addGroup(ICE_SHOT)
+		group.enabled = false
+		assert.are.equals(0, groupCount())
+	end)
+end)
diff --git a/src/Classes/SkillsTab.lua b/src/Classes/SkillsTab.lua
index ac8688c0b4..f8ff8f99a8 100644
--- a/src/Classes/SkillsTab.lua
+++ b/src/Classes/SkillsTab.lua
@@ -1576,9 +1576,16 @@ function SkillsTabClass:UpdateGlobalGemCountAssignments()
 			for _, gemInstance in ipairs(socketGroup.gemList) do
 				if gemInstance.enabled and not countGroup then
 					local grantedEffect = gemInstance.grantedEffect or gemInstance.gemData and gemInstance.gemData.grantedEffect
-					local provided = gemInstance.fromItem or gemInstance.fromTree or
-						grantedEffect and (grantedEffect.fromItem or grantedEffect.fromTree)
-					countGroup = not provided
+					-- Support gems never occupy a skill slot by themselves, so they must not
+					-- decide whether this group is counted. Without this, adding any support
+					-- to a group whose active skill is provided by an item or the tree (the
+					-- default weapon attack, a skill granted by a unique) flips the group to
+					-- counted, because the loop re-evaluates on every gem.
+					if not (grantedEffect and grantedEffect.support) then
+						local provided = gemInstance.fromItem or gemInstance.fromTree or
+							grantedEffect and (grantedEffect.fromItem or grantedEffect.fromTree)
+						countGroup = not provided
+					end
 				end
 				if gemInstance.gemData and gemInstance.enabled then
 					if GlobalGemAssignments[gemInstance.gemData.name] then