diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 68fad0daea..2183e5578d 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -1,7 +1,7 @@
 # Build, test and upload executables to GitHub
 # depends on pre-installed software; see image definitions:
 #  - https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2404-Readme.md
-#  - https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md
+#  - https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
 # We use these tools from the runner images: git, gcc/XCode/MSVC, swig, Tcl/Tk on MacOS, pkg-config
 
 # TODO: not building svs_viewer ('Cannot find GL, GLU, not building svs_viewer' and 'Cannot find opengl32, glu32, not building svs_viewer')
@@ -31,7 +31,7 @@ jobs:
           # Use v24 beta for now to get newer SWIG; TODO: change back to ubuntu-latest once it points to v24
           ubuntu-24.04,
           # latest available X86_64 target
-          macos-12,
+          macos-15,
           # latest is ARM
           macos-latest,
         ]
@@ -56,12 +56,12 @@ jobs:
         if: startsWith(matrix.os, 'ubuntu-')
         run: sudo apt-get update && sudo apt-get install tcl-dev
 
-      - name: Setup tcl (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup tcl (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install tcl-tk
 
-      - name: Setup SWIG (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup SWIG (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install swig
 
       - name: build
@@ -98,14 +98,15 @@ jobs:
           PYTHONUTF8: 1
         run: python3 TestPythonSML.py
 
-      # different install directory for macos-latest, since tcl-tk default in homebrew is now 9.0
-      - name: SML Tcl tests (macos-latest)
-        if: matrix.os == 'macos-latest'
+      # different install directory, since tcl-tk default in homebrew is now 9.0, and we only support 8
+      # see https://github.com/SoarGroup/Soar/issues/524
+      - name: SML Tcl tests (macos)
+        if: startsWith(matrix.os, 'macos')
         working-directory: ./out
         run: $(brew --prefix tcl-tk@8)/bin/tclsh TestTclSML.tcl
 
-      - name: SML Tcl tests
-        if: matrix.os != 'macos-latest'
+      - name: SML Tcl tests (ubuntu)
+        if: ! startsWith(matrix.os, 'macos')
         working-directory: ./out
         run: tclsh TestTclSML.tcl
 
@@ -285,7 +286,7 @@ jobs:
             # 20.04 to preserve compatibility with testing stage
             ubuntu-20.04,
             # latest available X86_64 target
-            macos-12,
+            macos-15,
             # latest is ARM
             macos-latest,
 
@@ -315,11 +316,11 @@ jobs:
       #   run: sudo apt-get update && sudo apt-get install tcl-dev
 
       # - name: Setup tcl (macos-latest)
-      #   if: matrix.os == 'macos-latest'
+      #   if: startsWith(matrix.os, 'macos')
       #   run: brew install tcl-tk
 
-      - name: Setup SWIG (macos-latest)
-        if: matrix.os == 'macos-latest'
+      - name: Setup SWIG (macos)
+        if: startsWith(matrix.os, 'macos')
         run: brew install swig
 
       - name: Setup SWIG (windows-latest)
@@ -371,7 +372,7 @@ jobs:
           # linux target which supports all python versions we want to install for
           - ubuntu-20.04
             # latest available X86_64 target
-          - macos-12
+          - macos-15
             # latest is ARM
           - macos-latest
           - windows-latest