diff --git a/bin/kaleidoscope-builder b/bin/kaleidoscope-builder
index 6f672190..88c4e3d5 100755
--- a/bin/kaleidoscope-builder
+++ b/bin/kaleidoscope-builder
@@ -49,10 +49,10 @@ build_paths() {
 }
 
 build_filenames () {
-    OUTPUT_FILE_PREFIX="${SKETCH}-${LIB_VERSION}"
-    HEX_FILE_PATH="${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}.hex"
-    HEX_FILE_WITH_BOOTLOADER_PATH="${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}-with-bootloader.hex"
-    ELF_FILE_PATH="${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}.elf"
+    OUTPUT_FILE_PREFIX="${OUTPUT_FILE_PREFIX:-${SKETCH}-${LIB_VERSION}}"
+    HEX_FILE_PATH="${HEX_FILE_PATH:-${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}.hex}"
+    HEX_FILE_WITH_BOOTLOADER_PATH="${HEX_FILE_WITH_BOOTLOADER_PATH:-${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}-with-bootloader.hex}"
+    ELF_FILE_PATH="${ELF_FILE_PATH:-${OUTPUT_PATH}/${OUTPUT_FILE_PREFIX}.elf}"
 }