diff --git a/lib/system.nim b/lib/system.nim
index 0fc7603490..ffdc59661d 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1703,19 +1703,19 @@ when not (notJSnotNims and defined(nimSeqsV2)):
   # Needed so modules imported by system (e.g. syncio) can reference these without guards.
   when notJSnotNims:
     # mm:refc: string = ptr NimStringDesc with data: UncheckedArray[char]
-    proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect.} =
+    proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect, tags: [].} =
       let ns = cast[NimString](s)
       if ns == nil: nil
       else: cast[ptr UncheckedArray[char]](addr ns.data[start])
-    proc endStore*(s: var string) {.inline, noSideEffect.} = discard
+    proc endStore*(s: var string) {.inline, noSideEffect, tags: [].} = discard
     template readRawData*(s: string; start = 0): ptr UncheckedArray[char] =
       let ns = cast[NimString](s)
       if ns == nil: nil
       else: cast[ptr UncheckedArray[char]](addr ns.data[start])
   else:
     # JS/nimscript: callers are guarded by whenNotVmJsNims/when not defined(js)
-    proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect.} = nil
-    proc endStore*(s: var string) {.inline, noSideEffect.} = discard
+    proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect, tags: [].} = nil
+    proc endStore*(s: var string) {.inline, noSideEffect, tags: [].} = discard
     template readRawData*(s: string; start = 0): ptr UncheckedArray[char] = nil
 
 when not defined(js):
diff --git a/lib/system/strs_v2.nim b/lib/system/strs_v2.nim
index b836b4c87d..b99b433257 100644
--- a/lib/system/strs_v2.nim
+++ b/lib/system/strs_v2.nim
@@ -187,7 +187,7 @@ proc nimPrepareStrMutationV2(s: var NimStringV2) {.compilerRtl, inl.} =
   if s.p != nil and (s.p.cap and strlitFlag) == strlitFlag:
     nimPrepareStrMutationImpl(s)
 
-proc prepareMutation*(s: var string) {.inline.} =
+proc prepareMutation*(s: var string) {.inline, tags: [].} =
   # string literals are "copy on write", so you need to call
   # `prepareMutation` before modifying the strings via `addr`.
   {.cast(noSideEffect).}:
@@ -216,14 +216,14 @@ func capacity*(self: string): int {.inline.} =
   let str = cast[ptr NimStringV2](unsafeAddr self)
   result = if str.p != nil: str.p.cap and not strlitFlag else: 0
 
-proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect.} =
+proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect, tags: [].} =
   ## Returns a writable pointer for bulk write of `ensuredLen` bytes starting at `start`.
   ## Call `endStore(s)` afterwards for portability.
   {.cast(noSideEffect).}: prepareMutation(s)
   if s.len == 0: nil
   else: cast[ptr UncheckedArray[char]](addr s[start])
 
-proc endStore*(s: var string) {.inline, noSideEffect.} =
+proc endStore*(s: var string) {.inline, noSideEffect, tags: [].} =
   ## No-op for non-SSO strings; call after bulk writes via `beginStore`.
   discard
 
diff --git a/lib/system/strs_v3.nim b/lib/system/strs_v3.nim
index 3bd0d2f136..b4e426908c 100644
--- a/lib/system/strs_v3.nim
+++ b/lib/system/strs_v3.nim
@@ -675,7 +675,7 @@ proc completeStore(s: var SmallString) {.compilerproc, inline.} =
 proc completeStore*(s: var string) {.inline.} =
   completeStore(cast[ptr SmallString](addr s)[])
 
-proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect.} =
+proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect, tags: [].} =
   ## Prepares `s` for a bulk write of `ensuredLen` bytes starting at `start`.
   ## The caller must ensure `s.len >= start + ensuredLen` (e.g. via `newString` or `setLen`).
   ## Call `endStore(s)` afterwards to sync the inline cache.
@@ -688,7 +688,7 @@ proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[
     else:
       result = cast[ptr UncheckedArray[char]](cast[uint](inlinePtr(ss[])) + uint(start))
 
-proc endStore*(s: var string) {.inline, noSideEffect.} =
+proc endStore*(s: var string) {.inline, noSideEffect, tags: [].} =
   ## Syncs the inline cache after bulk writes via `beginStore`. No-op for short/medium strings.
   {.cast(noSideEffect).}: completeStore(cast[ptr SmallString](addr s)[])