Make sure that MacPorts's Guile 3.0 is used, with the customized executable names.
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -94,9 +94,11 @@ if(NOT MSVC)
     find_package(Boost REQUIRED)
     find_package(PkgConfig REQUIRED)
 
-    pkg_check_modules(GUILE guile-2.2>=2.2.1)
-    if (NOT(GUILE_FOUND))
-        pkg_check_modules(GUILE guile-3.0>=3.0.0)
+    pkg_check_modules(GUILE guile-3.0>=3.0.0)
+
+    if (GUILE_FOUND)
+      pkg_get_variable(GUILE_EXEC guile-3.0 guile)
+      pkg_get_variable(GUILD_EXEC guile-3.0 guild)
     endif()
 
     pkg_check_modules(EIGEN REQUIRED eigen3>=3.2.92)
--- libfive/bind/guile/CMakeLists.txt
+++ libfive/bind/guile/CMakeLists.txt
@@ -28,10 +28,10 @@ foreach(SRC ${SRCS})
     #
     # Then, copy the file from Guile's compilation cache to the build directory
     execute_process(
-        COMMAND guile -c "(use-modules (system base compile))(format #t \"~A\" (compiled-file-name \"${FULL_SRC}\"))"
+        COMMAND ${GUILE_EXEC} -c "(use-modules (system base compile))(format #t \"~A\" (compiled-file-name \"${FULL_SRC}\"))"
         OUTPUT_VARIABLE CCACHE_FILE)
     add_custom_command(OUTPUT ${OUT}
-        COMMAND ${CMAKE_COMMAND} -E env LIBFIVE_FRAMEWORK_DIR=$<TARGET_FILE_DIR:libfive>/ LIBFIVE_STDLIB_DIR=$<TARGET_FILE_DIR:libfive-stdlib>/ guild compile -L${CMAKE_CURRENT_SOURCE_DIR} ${FULL_SRC}
+        COMMAND ${CMAKE_COMMAND} -E env LIBFIVE_FRAMEWORK_DIR=$<TARGET_FILE_DIR:libfive>/ LIBFIVE_STDLIB_DIR=$<TARGET_FILE_DIR:libfive-stdlib>/ ${GUILD_EXEC} compile -L${CMAKE_CURRENT_SOURCE_DIR} ${FULL_SRC}
         COMMAND ${CMAKE_COMMAND} -E copy ${CCACHE_FILE} ${CMAKE_CURRENT_BINARY_DIR}/${OUT}
         WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
         DEPENDS ${FULL_SRC} libfive libfive-stdlib)
@@ -45,7 +45,7 @@ if(UNIX)
     # Find the installation directory for compiled files
     if (NOT DEFINED GUILE_CCACHE_DIR)
         execute_process(
-            COMMAND guile -c "(format #t \"~A\" (%site-ccache-dir))"
+            COMMAND ${GUILE_EXEC} -c "(format #t \"~A\" (%site-ccache-dir))"
             OUTPUT_VARIABLE GUILE_CCACHE_DIR)
     endif()