diff --git a/package.json b/package.json
index 8a90807d6..b50ae32f1 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "open-plc-editor",
   "description": "OpenPLC Editor - IDE capable of creating programs for the OpenPLC Runtime",
-  "version": "4.2.10",
+  "version": "4.2.9",
   "license": "GPL-3.0",
   "author": {
     "name": "Autonomy Logic"
diff --git a/src/frontend/data/constants/app-version.ts b/src/frontend/data/constants/app-version.ts
index 3b99e5528..661f491e9 100644
--- a/src/frontend/data/constants/app-version.ts
+++ b/src/frontend/data/constants/app-version.ts
@@ -18,4 +18,4 @@
  * compares a per-deploy `BUILD_ID` (git commit SHA), not this version, so a
  * stale tab is detected on every deploy even without a version bump.
  */
-export const APP_VERSION = '4.2.10'
+export const APP_VERSION = '4.2.9'
diff --git a/src/frontend/store/__tests__/project-validation-variables.test.ts b/src/frontend/store/__tests__/project-validation-variables.test.ts
index 5c1611677..9fbb4ffb8 100644
--- a/src/frontend/store/__tests__/project-validation-variables.test.ts
+++ b/src/frontend/store/__tests__/project-validation-variables.test.ts
@@ -516,6 +516,28 @@ describe('updateVariableValidation', () => {
     },
   )
 
+  it.each([
+    ['BYTE', '%IB0'],
+    ['BYTE', '%QB1'],
+    ['BYTE', '%MB2'],
+    ['SINT', '%IB3'],
+    ['USINT', '%MB4'],
+  ])('accepts byte locations (I/Q/M) for %s type (%s)', (type, location) => {
+    const v = makeVariable('Test', type, '')
+    const result = updateVariableValidation([], { location }, v)
+    expect(result.ok).toBe(true)
+  })
+
+  it.each([
+    ['BYTE', '%IX0.0'], // bit location, wrong width for a byte type
+    ['SINT', '%IW0'], // word location, wrong width
+    ['BOOL', '%IB0'], // byte location, wrong width for a bit type
+  ])('rejects a cross-width location for %s (%s)', (type, location) => {
+    const v = makeVariable('Test', type, '')
+    const result = updateVariableValidation([], { location }, v)
+    expect(result.ok).toBe(false)
+  })
+
   it('returns ok: true when location is valid for WORD type', () => {
     const wordVar = makeVariable('Test', 'WORD', '')
     const result = updateVariableValidation([], { location: '%QW0' }, wordVar)
diff --git a/src/frontend/store/slices/project/validation/variables.ts b/src/frontend/store/slices/project/validation/variables.ts
index 24a570ac9..63186db6f 100644
--- a/src/frontend/store/slices/project/validation/variables.ts
+++ b/src/frontend/store/slices/project/validation/variables.ts
@@ -2,6 +2,7 @@ import type { PLCVariable } from '../../../../../middleware/shared/ports/types'
 import { DISALLOWED_LOCATION_CLASSES } from '../../../../utils/generate-iec-string-to-variables'
 import {
   BOOL_LOCATION_REGEX,
+  BYTE_LOCATION_REGEX,
   DWORD_LOCATION_REGEX,
   LWORD_LOCATION_REGEX,
   PLC_ADDRESS_PREFIX,
@@ -131,6 +132,10 @@ const variableLocationValidation = (variableLocation: string, variableType: stri
       const boolMatch = BOOL_LOCATION_REGEX.test(variableLocation) && variableLocation.split('.')[1] <= '7'
       return boolMatch
     }
+    case 'BYTE':
+    case 'SINT':
+    case 'USINT':
+      return BYTE_LOCATION_REGEX.test(variableLocation)
     case 'INT':
     case 'UINT':
     case 'WORD':
@@ -154,6 +159,10 @@ const variableLocationValidationErrorMessage = (variableType: string) => {
   switch (variableType.toUpperCase()) {
     case 'BOOL':
       return 'Valid locations: %QX0.0..7, %IX0.0..7, %MX0.0..7 (change the number to the desired location)'
+    case 'BYTE':
+    case 'SINT':
+    case 'USINT':
+      return 'Valid locations: %QB0, %IB0, %MB0 (change the number to the desired location)'
     case 'INT':
     case 'UINT':
     case 'WORD':
diff --git a/src/frontend/utils/PLC/address-constants/types.ts b/src/frontend/utils/PLC/address-constants/types.ts
index 5ab477d40..d856252de 100644
--- a/src/frontend/utils/PLC/address-constants/types.ts
+++ b/src/frontend/utils/PLC/address-constants/types.ts
@@ -2,6 +2,9 @@ export const PLC_ADDRESS_PREFIX = {
   BOOL_OUTPUT: '%QX',
   BOOL_INPUT: '%IX',
   BOOL_MEMORY: '%MX',
+  BYTE_OUTPUT: '%QB',
+  BYTE_INPUT: '%IB',
+  BYTE_MEMORY: '%MB',
   WORD_OUTPUT: '%QW',
   WORD_INPUT: '%IW',
   WORD_MEMORY: '%MW',
@@ -13,10 +16,14 @@ export const PLC_ADDRESS_PREFIX = {
   LWORD_MEMORY: '%ML',
 } as const
 
-// Accept every valid IEC area prefix — input (I), output (Q) and memory (M).
-// `%MX` memory bits are legitimate (e.g. Modbus coils) and were previously
-// rejected here, unlike the word-width regexes below which already allow M.
+// Each IEC size class accepts all three area prefixes — input (I), output (Q)
+// and memory (M) — matching what strucpp and the runtime image tables support:
+//   X = bit (BOOL), B = byte (BYTE/SINT/USINT), W = word (INT/UINT/WORD),
+//   D = dword (DINT/UDINT/REAL/DWORD), L = lword (LINT/ULINT/LREAL/LWORD).
+// NOTE: %MB (memory byte) is accepted here even though the runtime does not
+// yet back it (no byte_memory buffer) — a runtime fix is planned separately.
 export const BOOL_LOCATION_REGEX = /^%[QIM]X\d+\.\d$/
+export const BYTE_LOCATION_REGEX = /^%[QIM]B\d+$/
 export const WORD_LOCATION_REGEX = /^%[QIM]W\d+$/
 export const DWORD_LOCATION_REGEX = /^%[QIM]D\d+$/
 export const LWORD_LOCATION_REGEX = /^%[QIM]L\d+$/