diff --git a/BLAS/TESTING/CMakeLists.txt b/BLAS/TESTING/CMakeLists.txt
index 0ea274772..09882a90d 100644
--- a/BLAS/TESTING/CMakeLists.txt
+++ b/BLAS/TESTING/CMakeLists.txt
@@ -22,7 +22,7 @@ function(_add_blas_test name src test_input)
 endfunction()
 
 function(add_blas_test name source)
-  get_filename_component(baseNAME ${input_src} NAME_WE)
+  get_filename_component(baseNAME ${source} NAME_WE)
   set(test_input "${CMAKE_CURRENT_SOURCE_DIR}/${baseNAME}.in")
 
   if(BUILD_DEFAULT_API)
@@ -31,7 +31,7 @@ function(add_blas_test name source)
 
   if(BUILD_INDEX64_EXT_API)
     include(ExtendedAPIHelpers)
-    generate_64bit_suffixed_sources(${name}_64 source source_64)
+    generate_64bit_suffixed_sources(${name} source source_64)
 
     # Create 64-bit version of test input if it exists, replacing output
     # file names with their 64-bit counterparts
diff --git a/CMAKE/ExtendedAPIHelpers.cmake b/CMAKE/ExtendedAPIHelpers.cmake
index 0c83866f6..6757cae27 100644
--- a/CMAKE/ExtendedAPIHelpers.cmake
+++ b/CMAKE/ExtendedAPIHelpers.cmake
@@ -13,6 +13,8 @@ endif()
 # at build time in the Generate64BitSuffixedSource.cmake script.
 function(generate_64bit_suffixed_sources target source_list generated_sources)
   get_filename_component(destination "${target}_64_sources" ABSOLUTE BASE_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+  get_property(_generated_64bit_source_files GLOBAL PROPERTY EXTENDED_API_GENERATED_SOURCE_FILES)
+  set(new_generated_source_files)
   set(generated_source_files)
 
   foreach(source IN LISTS ${source_list})
@@ -27,28 +29,36 @@ function(generate_64bit_suffixed_sources target source_list generated_sources)
       continue()
     endif()
 
-    add_custom_command(
-      OUTPUT "${output_file}"
-      COMMAND
-        "${CMAKE_COMMAND}"
-        "-DINPUT_FILE=${source_abs}"
-        "-DOUTPUT_FILE=${output_file}"
-        -P "${EXTENDED_API_GENERATOR}"
-      DEPENDS
-        "${source_abs}"
-        "${EXTENDED_API_GENERATOR}"
-      COMMENT "Generating 64-bit extended API source for ${source}"
-      VERBATIM)
+    # Make sure we only have one custom command generating a given output file
+    if(NOT "${output_file}" IN_LIST _generated_64bit_source_files)
+      add_custom_command(
+        OUTPUT "${output_file}"
+        COMMAND
+          "${CMAKE_COMMAND}"
+          "-DINPUT_FILE=${source_abs}"
+          "-DOUTPUT_FILE=${output_file}"
+          -P "${EXTENDED_API_GENERATOR}"
+        DEPENDS
+          "${source_abs}"
+          "${EXTENDED_API_GENERATOR}"
+        COMMENT "Generating 64-bit extended API source for ${source}"
+        VERBATIM)
+
+      list(APPEND new_generated_source_files "${output_file}")
+    endif()
 
     list(APPEND generated_source_files "${output_file}")
   endforeach()
 
-  if(generated_source_files)
+  # Make sure each generated source file is only part of one target to
+  # avoid multiple targets trying to generate the same file
+  if(new_generated_source_files)
     add_custom_target("${target}_64bit_codegen" ALL
-      DEPENDS ${generated_source_files}
+      DEPENDS ${new_generated_source_files}
       COMMENT "Generating 64-bit suffixed sources for target ${target}")
     add_dependencies(64bit_codegen "${target}_64bit_codegen")
-    set_source_files_properties(${generated_source_files} PROPERTIES GENERATED TRUE)
+
+    set_property(GLOBAL APPEND PROPERTY EXTENDED_API_GENERATED_SOURCE_FILES ${new_generated_source_files})
   endif()
 
   set(${generated_sources} ${generated_source_files} PARENT_SCOPE)
diff --git a/TESTING/EIG/CMakeLists.txt b/TESTING/EIG/CMakeLists.txt
index 0c9792b67..5f676e057 100644
--- a/TESTING/EIG/CMakeLists.txt
+++ b/TESTING/EIG/CMakeLists.txt
@@ -113,11 +113,16 @@ function(add_eig_executable name)
 
   if(BUILD_INDEX64_EXT_API)
     include(ExtendedAPIHelpers)
-    generate_64bit_suffixed_sources(${name}_64 ${sources} sources_64)
+    generate_64bit_suffixed_sources(${name} sources sources_64)
 
     add_executable(${name}_64 ${sources_64})
     target_compile_options(${name}_64 PRIVATE ${FOPT_ILP64})
     target_link_libraries(${name}_64 ${TMGLIB} ${LAPACK_LIBRARIES} ${BLAS_LIBRARIES})
+
+    # Add depedency to the global codegen target. Since we reuse the same
+    # generated source file for multiple tests, the generation could be
+    # triggered by multiple targets when building in parallel.
+    add_dependencies(${name}_64 64bit_codegen)
   endif()
 endfunction()
 
diff --git a/TESTING/LIN/CMakeLists.txt b/TESTING/LIN/CMakeLists.txt
index 6b3ba1b87..15f9671d9 100644
--- a/TESTING/LIN/CMakeLists.txt
+++ b/TESTING/LIN/CMakeLists.txt
@@ -254,11 +254,16 @@ function(add_lin_executable name)
 
   if(BUILD_INDEX64_EXT_API)
     include(ExtendedAPIHelpers)
-    generate_64bit_suffixed_sources(${name}_64 sources sources_64)
+    generate_64bit_suffixed_sources(${name} sources sources_64)
 
     add_executable(${name}_64 ${sources_64})
     target_compile_options(${name}_64 PRIVATE ${FOPT_ILP64})
     target_link_libraries(${name}_64 ${TMGLIB} ${LAPACK_LIBRARIES} ${BLAS_LIBRARIES})
+
+    # Add depedency to the global codegen target. Since we reuse the same
+    # generated source file for multiple tests, the generation could be
+    # triggered by multiple targets when building in parallel.
+    add_dependencies(${name}_64 64bit_codegen)
   endif()
 endfunction()