diff --git a/compiler/llstream.nim b/compiler/llstream.nim
index 77cb94eb7e..98fa1efdfe 100644
--- a/compiler/llstream.nim
+++ b/compiler/llstream.nim
@@ -163,8 +163,7 @@ proc llReadFromStdin(s: PLLStream, buf: pointer, bufLen: int): int =
   inc(s.lineOffset)
   result = min(bufLen, s.s.len - s.rd)
   if result > 0:
-    let (sdata, _) = readRawData(s.s)
-    copyMem(buf, addr sdata[s.rd], result)
+    copyMem(buf, readRawData(s.s, s.rd), result)
     inc(s.rd, result)
 
 proc llStreamRead*(s: PLLStream, buf: pointer, bufLen: int): int =
@@ -174,8 +173,7 @@ proc llStreamRead*(s: PLLStream, buf: pointer, bufLen: int): int =
   of llsString:
     result = min(bufLen, s.s.len - s.rd)
     if result > 0:
-      let (sdata, _) = readRawData(s.s)
-      copyMem(buf, addr sdata[s.rd], result)
+      copyMem(buf, readRawData(s.s, s.rd), result)
       inc(s.rd, result)
   of llsFile:
     result = readBuffer(s.f, buf, bufLen)
diff --git a/lib/pure/streams.nim b/lib/pure/streams.nim
index 1c31ca0752..a1fffa5d95 100644
--- a/lib/pure/streams.nim
+++ b/lib/pure/streams.nim
@@ -1226,8 +1226,7 @@ else: # after 1.3 or JS not defined
       jsOrVmBlock:
         buffer[slice.a..<slice.a+result] = s.data[s.pos..<s.pos+result]
       do:
-        let (srcData, _) = readRawData(s.data)
-        copyMem(beginStore(buffer, result, slice.a), addr srcData[s.pos], result)
+        copyMem(beginStore(buffer, result, slice.a), readRawData(s.data, s.pos), result)
         endStore(buffer)
       inc(s.pos, result)
     else:
@@ -1244,8 +1243,7 @@ else: # after 1.3 or JS not defined
           raise newException(Defect, "could not read string stream, " &
             "did you use a non-string buffer pointer?", getCurrentException())
       elif not defined(nimscript):
-        let (srcData, _) = readRawData(s.data)
-        copyMem(buffer, addr srcData[s.pos], result)
+        copyMem(buffer, readRawData(s.data, s.pos), result)
       inc(s.pos, result)
     else:
       result = 0
@@ -1261,8 +1259,7 @@ else: # after 1.3 or JS not defined
           raise newException(Defect, "could not peek string stream, " &
             "did you use a non-string buffer pointer?", getCurrentException())
       elif not defined(nimscript):
-        let (srcData, _) = readRawData(s.data)
-        copyMem(buffer, addr srcData[s.pos], result)
+        copyMem(buffer, readRawData(s.data, s.pos), result)
     else:
       result = 0
 
diff --git a/lib/pure/strutils.nim b/lib/pure/strutils.nim
index ae083a2201..ca6d33e48b 100644
--- a/lib/pure/strutils.nim
+++ b/lib/pure/strutils.nim
@@ -1983,7 +1983,7 @@ func find*(s: string, sub: char, start: Natural = 0, last = -1): int {.rtl,
     when hasCStringBuiltin:
       let length = last-start+1
       if length > 0:
-        let (sdata, _) = readRawData(s)
+        let sdata = readRawData(s)
         let found = c_memchr(addr sdata[start], cint(sub), cast[csize_t](length))
         if not found.isNil:
           return cast[int](found) -% cast[int](sdata)
@@ -2042,9 +2042,8 @@ func find*(s, sub: string, start: Natural = 0, last = -1): int {.rtl,
     when declared(memmem):
       let subLen = sub.len
       if last < 0 and start < s.len and subLen != 0:
-        let (sdata, _) = readRawData(s)
-        let (subdata, _) = readRawData(sub)
-        let found = memmem(addr sdata[start], csize_t(s.len - start), subdata, csize_t(subLen))
+        let sdata = readRawData(s)
+        let found = memmem(addr sdata[start], csize_t(s.len - start), readRawData(sub), csize_t(subLen))
         result = if not found.isNil:
             cast[int](found) -% cast[int](sdata)
           else:
diff --git a/lib/std/syncio.nim b/lib/std/syncio.nim
index 153b79c660..70a0c711cb 100644
--- a/lib/std/syncio.nim
+++ b/lib/std/syncio.nim
@@ -496,7 +496,7 @@ proc readLine*(f: File, line: var string): bool {.tags: [ReadIOEffect],
       checkErr(f)
       break
 
-    let (lineData, _) = readRawData(line)
+    let lineData = readRawData(line)
     let m = c_memchr(addr lineData[pos], cint('\L'), cast[csize_t](sp))
     if m != nil:
       # \l found: Could be our own or the one by fgets, in any case, we're done
diff --git a/lib/system.nim b/lib/system.nim
index 37fc344929..0fc7603490 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1699,14 +1699,24 @@ when notJSnotNims and defined(nimSeqsV2):
   include "system/seqs_v2"
 
 when not (notJSnotNims and defined(nimSeqsV2)):
-  # Fallback stubs for js/nimscript/non-V2 backends where strs_v2/v3 is not included.
-  # These are needed so that modules imported by system (e.g. syncio) can reference
-  # beginStore/endStore/readRawData without a 'when declared(...)' guard.
-  proc beginStore*(s: var string; ensuredLen: int; start = 0): ptr UncheckedArray[char] {.inline, noSideEffect.} =
-    result = cast[ptr UncheckedArray[char]](addr s[start])
-  proc endStore*(s: var string) {.inline, noSideEffect.} = discard
-  template readRawData*(s: string): (ptr UncheckedArray[char], int) =
-    (cast[ptr UncheckedArray[char]](nil), s.len)
+  # Fallback implementations for backends where strs_v2/v3 is not included.
+  # 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.} =
+      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
+    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
+    template readRawData*(s: string; start = 0): ptr UncheckedArray[char] = nil
 
 when not defined(js):
   template newSeqImpl(T, len) =
@@ -2975,8 +2985,7 @@ proc substr*(s: string; first, last: int): string = # A bug with `magic: Slice`
   result = newStringUninit(L)
   whenNotVmJsNims():
     if L > 0:
-      let (src, _) = readRawData(s)
-      copyMem(beginStore(result, L), addr src[first], L)
+      copyMem(beginStore(result, L), readRawData(s, first), L)
       endStore(result)
   do:
     for i in 0..<L:
diff --git a/lib/system/strs_v2.nim b/lib/system/strs_v2.nim
index 596cec98a1..b836b4c87d 100644
--- a/lib/system/strs_v2.nim
+++ b/lib/system/strs_v2.nim
@@ -227,10 +227,10 @@ proc endStore*(s: var string) {.inline, noSideEffect.} =
   ## No-op for non-SSO strings; call after bulk writes via `beginStore`.
   discard
 
-template readRawData*(s: string): (ptr UncheckedArray[char], int) =
-  ## Returns `(dataPtr, length)` for read-only raw access to string data.
+template readRawData*(s: string; start = 0): ptr UncheckedArray[char] =
+  ## Returns a pointer to `s[start]` for read-only raw access.
   ## Template ensures no copy of `s`; ptr is valid while `s` is alive.
-  let p = if s.len == 0: nil else: cast[ptr UncheckedArray[char]](unsafeAddr s[0])
-  (p, s.len)
+  let str = cast[ptr NimStringV2](unsafeAddr s)
+  if str.p == nil: nil else: cast[ptr UncheckedArray[char]](addr str.p.data[start])
 
 {.pop.}
diff --git a/lib/system/strs_v3.nim b/lib/system/strs_v3.nim
index 43a80d36cd..3bd0d2f136 100644
--- a/lib/system/strs_v3.nim
+++ b/lib/system/strs_v3.nim
@@ -692,19 +692,17 @@ proc endStore*(s: var string) {.inline, noSideEffect.} =
   ## Syncs the inline cache after bulk writes via `beginStore`. No-op for short/medium strings.
   {.cast(noSideEffect).}: completeStore(cast[ptr SmallString](addr s)[])
 
-proc rawDataImpl(ss: ptr SmallString): (ptr UncheckedArray[char], int) {.inline.} =
+proc rawDataImpl(ss: ptr SmallString; start: int): ptr UncheckedArray[char] {.inline, noSideEffect, raises: [].} =
   let slen = ssLen(ss[])
   let actualLen = if slen > PayloadSize: ss[].more.fullLen else: slen
-  let p =
-    if actualLen == 0: nil
-    elif slen > PayloadSize: cast[ptr UncheckedArray[char]](addr ss[].more.data[0])
-    else: inlinePtr(ss[])
-  (p, actualLen)
+  if actualLen == 0: nil
+  elif slen > PayloadSize: cast[ptr UncheckedArray[char]](addr ss[].more.data[start])
+  else: cast[ptr UncheckedArray[char]](cast[uint](inlinePtr(ss[])) + uint(start))
 
-template readRawData*(s: string): (ptr UncheckedArray[char], int) =
-  ## Returns `(dataPtr, length)` for read-only raw access to string data.
+template readRawData*(s: string; start = 0): ptr UncheckedArray[char] =
+  ## Returns a pointer to `s[start]` for read-only raw access.
   ## Template ensures no copy of `s` is made; ptr is valid while `s` is alive.
-  rawDataImpl(cast[ptr SmallString](unsafeAddr s))
+  rawDataImpl(cast[ptr SmallString](unsafeAddr s), start)
 
 # These take `string` (tyString) so the codegen uses them directly, bypassing
 # strmantle.nim's versions which go through nimStrLen/nimStrAtMutV3 compilerproc calls.