diff --git a/lambda/compiler.rb b/lambda/compiler.rb
index 9e9b8848552b..58ab0eaef8d2 100644
--- a/lambda/compiler.rb
+++ b/lambda/compiler.rb
@@ -35,7 +35,7 @@ def compile_board(board, keymap_data:, kconfig_data:, include_static_rhs: false)
       compile_command = ['compileZmk', '-b', board]
 
       if keymap_data
-        validate_devicetree!(keymap_data)
+        dts_parse_errors = validate_devicetree!(keymap_data)
         File.open('build.keymap', 'w') { |io| io.write(keymap_data) }
         compile_command << '-k' << './build.keymap'
       end
@@ -67,6 +67,13 @@ def compile_board(board, keymap_data:, kconfig_data:, include_static_rhs: false)
         raise CompileError.new('Compile failed to produce result binary', status: 500, log: compile_output)
       end
 
+      if dts_parse_errors
+        # DTS validation failed to parse the DTS, yet the Zephyr build
+        # nonetheless succeeded. We can't allow returning the result, since we
+        # were unable to check it for unsafe dts sections.
+        raise CompileError.new('Syntax error validating device-tree input', log: dts_parse_errors)
+      end
+
       result = File.read('zmk.uf2')
 
       [result, compile_output]
@@ -84,7 +91,11 @@ def validate_devicetree!(dtsi)
       Open3.capture3({}, 'dts2yml', unsetenv_others: true, stdin_data: dts)
 
     unless status.success?
-      raise CompileError.new('Syntax error checking device-tree input', log: stderr.split("\n"))
+      # The error output from dtc is much harder to understand than Zephyr's
+      # errors, and the line numbers don't match up due to preprocessing. Rather
+      # than raising these now, return the error output in order that it's only
+      # used in the case that the Zephyr build doesn't itself error.
+      return stderr.split("\n")
     end
 
     data =
@@ -101,6 +112,8 @@ def validate_devicetree!(dtsi)
       raise CompileError.new(
               "Device-tree included the non-permitted root sections: #{invalid_sections.inspect}", log: [])
     end
+
+    nil
   end
 
   # Lambda is single-process per container, and we get substantial speedups