diff --git a/spec/System/TestItemMods_spec.lua b/spec/System/TestItemMods_spec.lua
index 3aa079e67b9..4034535a947 100644
--- a/spec/System/TestItemMods_spec.lua
+++ b/spec/System/TestItemMods_spec.lua
@@ -1103,4 +1103,22 @@ describe("TetsItemMods", function()
 		assert.is_not_nil(sentinel)
 		assert.are.equals(1, countSupport(sentinel, "SupportMinionDamage"))
 	end)
+	-- #10310
+	it("an item's own ExtraSupport for a support gem does not disable that support elsewhere", function()
+		addItem("Supporting Gloves\nSpiked Gloves\nGrants Level 20 Sunder")
+		build.skillsTab:PasteSocketGroup("Slot: Gloves\nFist of War 20/0  1\n")
+		runCallback("OnFrame")
+
+		local sunder = findActiveSkill("Sunder")
+		assert.is_not_nil(sunder)
+		assert.is_true(hasSupport(sunder, "SupportFistofWar"))
+
+		addItem("Breaking Body Armour\nSimple Robe\nSkills from Equipped Body Armour are Supported by Level 20 Fist of War")
+		build.skillsTab:PasteSocketGroup("Slot: Body Armour\nHeavy Strike 20/0  1\n")
+		runCallback("OnFrame")
+
+		sunder = findActiveSkill("Sunder")
+		assert.is_not_nil(sunder)
+		assert.is_true(hasSupport(sunder, "SupportFistofWar"))
+	end)
 end)
diff --git a/src/Modules/CalcSetup.lua b/src/Modules/CalcSetup.lua
index 70301168360..e1fc9da72bc 100644
--- a/src/Modules/CalcSetup.lua
+++ b/src/Modules/CalcSetup.lua
@@ -1600,6 +1600,12 @@ function calcs.initEnv(build, mode, override, specEnv)
 		local supportLists = { }
 		local groupCfgList = { }
 		local processedSockets = {}
+		-- granted effects normally refer to the global tables in data.skills,
+		-- which means that modifying them will do so permanently until the
+		-- client is restarted. this avoids that by mapping from the original
+		-- table to a modified table.
+		---@type table<table, table>
+		local fromItemReplacements = {}
 		-- Process support gems adding them to applicable support lists
 		for index, group in ipairs(build.skillsTab.socketGroupList) do
 			local slot = group.slot and build.itemsTab.slots[group.slot]
@@ -1634,7 +1640,12 @@ function calcs.initEnv(build, mode, override, specEnv)
 						grantedEffect = env.data.skills["Support"..value.skillId]
 					end
 					if value and grantedEffect then -- Only item ExtraSupport gems should be flagged as fromItem. Imbued gems do not pass this check
-						grantedEffect.fromItem = true
+						if not fromItemReplacements[grantedEffect] then
+							local taggedGrantedEffect = copyTable(grantedEffect, true)
+							taggedGrantedEffect.fromItem = true
+							fromItemReplacements[grantedEffect] = taggedGrantedEffect
+						end
+						grantedEffect = fromItemReplacements[grantedEffect]
 					end
 					if grantedEffect then
 						for _, targetList in ipairs(targetListList) do
diff --git a/src/Modules/Common.lua b/src/Modules/Common.lua
index b71053f5f24..6db5add9d31 100644
--- a/src/Modules/Common.lua
+++ b/src/Modules/Common.lua
@@ -543,7 +543,7 @@ function specCopy(env)
 end
 
 -- Wipe all keys from the table and return it, or return a new table if no table
--- provided. This is useful to avoid alllocations in hot paths if a table can be reused. Using LuaJIT's `table.clear()` is another alternative to this, but this performs similarly on small tables, or tables which are often already empty.
+-- provided. This is useful to avoid allocations in hot paths if a table can be reused. Using LuaJIT's `table.clear()` is another alternative to this, but this performs similarly on small tables, or tables which are often already empty.
 ---@param tbl table?
 ---@return table tbl
 function wipeTable(tbl)