diff --git a/.github/workflows/build-toolchain.yml b/.github/workflows/build-toolchain.yml
index 04211da6..948ee1cd 100644
--- a/.github/workflows/build-toolchain.yml
+++ b/.github/workflows/build-toolchain.yml
@@ -227,14 +227,14 @@ jobs:
             branch_name="release/$branch_version_string"
           fi
 
-          repo init --quiet --groups default --depth 1 -u https://github.com/compnerd/swift-build -b $branch_name
+          repo init --quiet --groups default --depth 1 -u https://github.com/thebrowsercompany/swift-build -b hiroshi/mimallocarm64
           repo sync --quiet --no-clone-bundle --no-tags --jobs $(nproc --all)
 
           if [[ "${{ inputs.swift_tag }}" != "" ]] ; then
             tee -a "${GITHUB_OUTPUT}" <<-EOF
           indexstore_db_revision=refs/tags/${{ inputs.swift_tag }}
           llvm_project_revision=refs/tags/${{ inputs.swift_tag }}
-          mimalloc_revision=refs/tags/v2.1.7
+          mimalloc_revision=refs/tags/v3.0.1
           sourcekit_lsp_revision=refs/tags/${{ inputs.swift_tag }}
           swift_revision=refs/tags/${{ inputs.swift_tag }}
           swift_argument_parser_revision=refs/tags/1.4.0
diff --git a/.github/workflows/swift-toolchain.yml b/.github/workflows/swift-toolchain.yml
index b06e4db7..e0098255 100644
--- a/.github/workflows/swift-toolchain.yml
+++ b/.github/workflows/swift-toolchain.yml
@@ -3430,22 +3430,31 @@ jobs:
           }
 
       - uses: actions/checkout@v4
-        if: matrix.arch == 'amd64'
         with:
           repository: microsoft/mimalloc
           ref: ${{ inputs.mimalloc_revision }}
           path: ${{ github.workspace }}/SourceCache/mimalloc
 
       - name: Build and apply mimalloc
-        if: matrix.arch == 'amd64'
         run: |
+          $HostMSArch = if ("${{ matrix.arch }}" -eq "amd64") { "x64" } else { "arm64" }
+          $HostSuffix = if ("${{ matrix.arch }}" -eq "amd64") { "" } else { "-arm64" }
+          $BuildSuffix = if ("${{ inputs.build_arch }}" -eq "amd64") { "" } else { "-arm64" }
           # Reference: https://github.com/microsoft/mimalloc/tree/dev/bin#minject
-          msbuild ${{ github.workspace }}\SourceCache\mimalloc\ide\vs2022\mimalloc.sln -p:Configuration=Release
+          msbuild ${{ github.workspace }}\SourceCache\mimalloc\ide\vs2022\mimalloc.sln -p:Configuration=Release -p:Platform=$HostMSArch
           $ToolchainBin = "${{ github.workspace }}\BuildRoot\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin"
-          Copy-Item -Path "${{ github.workspace }}\SourceCache\mimalloc\out\msvc-x64\Release\mimalloc-override.dll" `
-            -Destination "$ToolchainBin"
-          Copy-Item -Path "${{ github.workspace }}\SourceCache\mimalloc\out\msvc-x64\Release\mimalloc-redirect.dll" `
+          Copy-Item -Path "${{ github.workspace }}\SourceCache\mimalloc\out\msvc-$HostMSArch\Release\mimalloc.dll" `
             -Destination "$ToolchainBin"
+          # We always use the file name "mimalloc-redirect.dll" at the
+          # destination even on arm64. Copy and rename as such. This
+          # is because the arm64 minject, which would use the "-arm64"
+          # suffix name, won't run on win/x64 but the x64 minject,
+          # which uses the unsuffixed name, runs both on x64 and arm64
+          # in the cross-compile build.
+          Copy-Item -Path "${{ github.workspace }}\SourceCache\mimalloc\out\msvc-$HostMSArch\Release\mimalloc-redirect$HostSuffix.dll" `
+            -Destination "$ToolchainBin/mimalloc-redirect$BuildSuffix.dll"
+            #-Destination "$ToolchainBin"
+            #-Destination "$ToolchainBin/mimalloc-redirect.dll"
           $MimallocExecutables = @("swift.exe",
                                    "swiftc.exe",
                                    "swift-driver.exe",
@@ -3458,14 +3467,16 @@ jobs:
                                    "ld.lld.exe",
                                    "ld64.lld.exe")
           foreach ($Exe in $MimallocExecutables) {
-            # Binary-patch in place
-            ${{ github.workspace }}\SourceCache\mimalloc\bin\minject -f -i -v "$ToolchainBin\$Exe"
+            # Binary-patch in place. This always uses the x64 minject even on
+            # win/arm64 via emulation for the above reason.
+            & "${{ github.workspace }}\SourceCache\mimalloc\bin\minject$BuildSuffix" -f -i -v "$ToolchainBin\$Exe"
             # Log the import table
-            ${{ github.workspace }}\SourceCache\mimalloc\bin\minject -l "$ToolchainBin\$Exe"
+            & "${{ github.workspace }}\SourceCache\mimalloc\bin\minject$BuildSuffix" -l "$ToolchainBin\$Exe"
           }
 
       - name: Package Build Tools
         run: |
+          $MIMALLOC_REDIRECT_SUFFIX = = if ("${{ inputs.build_arch }}" -eq "amd64") { "" } else { "-arm64" }
           msbuild -nologo -restore -maxCpuCount `
               -p:BaseOutputPath=${{ github.workspace }}\BinaryCache\installer\ `
               -p:Configuration=Release `
@@ -3473,7 +3484,8 @@ jobs:
               -p:CERTIFICATE=${env:CERTIFICATE} `
               -p:PASSPHRASE=${{ secrets.PASSPHRASE }} `
               -p:TOOLCHAIN_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
-              -p:ENABLE_MIMALLOC=${{ matrix.arch == 'amd64' && 'true' || 'false' }} `
+              -p:ENABLE_MIMALLOC=true `
+              -p:MIMALLOC_REDIRECT_SUFFIX=$MIMALLOC_REDIRECT_SUFFIX `
               -p:ProductArchitecture=${{ matrix.arch }} `
               -p:ProductVersion=${{ inputs.swift_version }} `
               ${{ github.workspace }}/SourceCache/swift-installer-scripts/platforms/Windows/bld/bld.wixproj
diff --git a/default.xml b/default.xml
index 44ce0437..2376f51e 100644
--- a/default.xml
+++ b/default.xml
@@ -30,7 +30,7 @@
   <project remote="github" name="swiftlang/swift-format" path="swift-format" />
   <project remote="github" name="swiftlang/swift-foundation" path="swift-foundation" />
   <project remote="github" name="swiftlang/swift-foundation-icu" path="swift-foundation-icu" />
-  <project remote="github" name="swiftlang/swift-installer-scripts" path="swift-installer-scripts" />
+  <project remote="github" name="hjyamauchi/swift-installer-scripts" path="swift-installer-scripts" revision="mimallocv3.0.1" />
   <project remote="github" name="swiftlang/swift-llbuild" path="llbuild" />
   <project remote="github" name="swiftlang/swift-lmdb" path="swift-lmdb" />
   <project remote="github" name="apple/swift-log" path="swift-log" groups="notdefault" />
@@ -63,7 +63,7 @@
 
   <project remote="github" name="madler/zlib" path="zlib" revision="refs/tags/v1.3.1" />
 
-  <project remote="github" name="microsoft/mimalloc" path="mimalloc" revision="refs/tags/v2.1.7" />
+  <project remote="github" name="microsoft/mimalloc" path="mimalloc" revision="refs/tags/v3.0.1" />
 
   <project remote="github" name="ninja-build/ninja" path="ninja" groups="notdefault,dependencies" revision="master" />
 </manifest>