diff --git a/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java b/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
index 01c617776..6cf7690c6 100644
--- a/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
+++ b/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
@@ -37,10 +37,12 @@
 import com.sun.tools.javac.parser.Tokens.TokenKind;
 import com.sun.tools.javac.tree.JCTree.JCCompilationUnit;
 import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.JCDiagnostic;
 import com.sun.tools.javac.util.Log;
 import com.sun.tools.javac.util.Log.DeferredDiagnosticHandler;
 import com.sun.tools.javac.util.Options;
 import java.io.IOException;
+import java.lang.reflect.Method;
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -53,6 +55,7 @@
 import javax.tools.JavaFileObject;
 import javax.tools.JavaFileObject.Kind;
 import javax.tools.SimpleJavaFileObject;
+import org.jspecify.annotations.Nullable;
 
 /** {@code JavaInput} extends {@link Input} to represent a Java input document. */
 public final class JavaInput extends Input {
@@ -364,7 +367,15 @@ public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOExcept
         });
     DeferredDiagnosticHandler diagnostics = new DeferredDiagnosticHandler(log);
     ImmutableList<RawTok> rawToks = JavacTokens.getTokens(text, context, stopTokens);
-    if (diagnostics.getDiagnostics().stream().anyMatch(d -> d.getKind() == Diagnostic.Kind.ERROR)) {
+    Collection<JCDiagnostic> ds;
+    try {
+      @SuppressWarnings("unchecked")
+      var extraLocalForSuppression = (Collection<JCDiagnostic>) GET_DIAGNOSTICS.invoke(diagnostics);
+      ds = extraLocalForSuppression;
+    } catch (ReflectiveOperationException e) {
+      throw new LinkageError(e.getMessage(), e);
+    }
+    if (ds.stream().anyMatch(d -> d.getKind() == Diagnostic.Kind.ERROR)) {
       return ImmutableList.of(new Tok(0, "", "", 0, 0, true, null)); // EOF
     }
     int kN = 0;
@@ -471,6 +482,16 @@ public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOExcept
     return ImmutableList.copyOf(toks);
   }
 
+  private static final Method GET_DIAGNOSTICS = getGetDiagnostics();
+
+  private static @Nullable Method getGetDiagnostics() {
+    try {
+      return DeferredDiagnosticHandler.class.getMethod("getDiagnostics");
+    } catch (NoSuchMethodException e) {
+      throw new LinkageError(e.getMessage(), e);
+    }
+  }
+
   private static int updateColumn(int columnI, String originalTokText) {
     Integer last = Iterators.getLast(Newlines.lineOffsetIterator(originalTokText));
     if (last > 0) {