diff --git a/open-java-format-spi/src/main/java/com/palantir/javaformat/java/FormatterDiagnostic.java b/open-java-format-spi/src/main/java/com/palantir/javaformat/java/FormatterDiagnostic.java
index 3f4794ab5..26f0a6ace 100644
--- a/open-java-format-spi/src/main/java/com/palantir/javaformat/java/FormatterDiagnostic.java
+++ b/open-java-format-spi/src/main/java/com/palantir/javaformat/java/FormatterDiagnostic.java
@@ -48,7 +48,7 @@ public int line() {
     }
 
     /**
-     * Returns the 0-indexed column number on which the error occurred, or {@code -1} if the error does not have a
+     * Returns the 1-indexed column number on which the error occurred, or {@code -1} if the error does not have a
      * column.
      */
     public int column() {
@@ -67,8 +67,7 @@ public String toString() {
             sb.append(lineNumber).append(':');
         }
         if (column >= 0) {
-            // internal column numbers are 0-based, but diagnostics use 1-based indexing by convention
-            sb.append(column + 1).append(':');
+            sb.append(column).append(':');
         }
         if (lineNumber >= 0 || column >= 0) {
             sb.append(' ');
diff --git a/open-java-format/src/test/java/com/palantir/javaformat/java/DiagnosticTest.java b/open-java-format/src/test/java/com/palantir/javaformat/java/DiagnosticTest.java
index 8002e269d..d5dae53d2 100644
--- a/open-java-format/src/test/java/com/palantir/javaformat/java/DiagnosticTest.java
+++ b/open-java-format/src/test/java/com/palantir/javaformat/java/DiagnosticTest.java
@@ -78,7 +78,7 @@ public void parseError() throws Exception {
 
         int result = main.format(path.toString());
         assertThat(stdout.toString()).isEmpty();
-        assertThat(stderr.toString()).contains("InvalidSyntax.java:2:29: error: <identifier> expected");
+        assertThat(stderr.toString()).contains("InvalidSyntax.java:2:28: error: <identifier> expected");
         assertThat(result).isEqualTo(2);
     }
 
@@ -116,7 +116,7 @@ public void oneFileParseError() throws Exception {
 
         int result = main.format(pathOne.toString(), pathTwo.toString());
         assertThat(stdout.toString()).isEqualTo(two);
-        assertThat(stderr.toString()).contains("One.java:1:13: error: reached end of file");
+        assertThat(stderr.toString()).contains("One.java:1:12: error: reached end of file");
         assertThat(result).isEqualTo(2);
     }
 
@@ -137,7 +137,7 @@ public void oneFileParseErrorReplace() throws Exception {
 
         int result = main.format("-i", pathOne.toString(), pathTwo.toString());
         assertThat(stdout.toString()).isEmpty();
-        assertThat(stderr.toString()).contains("One.java:1:14: error: class, interface");
+        assertThat(stderr.toString()).contains("One.java:1:13: error: class, interface");
         assertThat(result).isEqualTo(2);
         // don't edit files with parse errors
         assertThat(Files.readAllLines(pathOne, UTF_8)).containsExactly("class One {}}");
@@ -159,7 +159,7 @@ public void parseError2() throws FormatterException, IOException, UsageException
         int exitCode = main.format(args);
 
         assertThat(exitCode).isEqualTo(2);
-        assertThat(err.toString()).contains("A.java:2:6: error: ';' expected");
+        assertThat(err.toString()).contains("A.java:2:5: error: ';' expected");
     }
 
     @Test
@@ -174,7 +174,7 @@ public void parseErrorStdin() throws FormatterException, IOException, UsageExcep
         int exitCode = main.format(args);
 
         assertThat(exitCode).isEqualTo(2);
-        assertThat(err.toString()).contains("<stdin>:2:6: error: ';' expected");
+        assertThat(err.toString()).contains("<stdin>:2:5: error: ';' expected");
     }
 
     @Test
@@ -192,7 +192,7 @@ public void lexError2() throws FormatterException, IOException, UsageException {
         int exitCode = main.format(args);
 
         assertThat(exitCode).isEqualTo(2);
-        assertThat(err.toString()).contains("A.java:2:5: error: unclosed character literal");
+        assertThat(err.toString()).contains("A.java:2:4: error: unclosed character literal");
     }
 
     @Test
@@ -206,6 +206,6 @@ public void lexErrorStdin() throws FormatterException, IOException, UsageExcepti
         int exitCode = main.format(args);
 
         assertThat(exitCode).isEqualTo(2);
-        assertThat(err.toString()).contains("<stdin>:2:5: error: unclosed character literal");
+        assertThat(err.toString()).contains("<stdin>:2:4: error: unclosed character literal");
     }
 }
diff --git a/open-java-format/src/test/java/com/palantir/javaformat/java/MainTest.java b/open-java-format/src/test/java/com/palantir/javaformat/java/MainTest.java
index a87238af0..73b5efd8b 100644
--- a/open-java-format/src/test/java/com/palantir/javaformat/java/MainTest.java
+++ b/open-java-format/src/test/java/com/palantir/javaformat/java/MainTest.java
@@ -351,7 +351,7 @@ public void importRemoveErrorParseError() throws Exception {
                     new PrintWriter(err, true),
                     new ByteArrayInputStream(joiner.join(input).getBytes(UTF_8)));
             assertThat(main.format("-")).isEqualTo(2);
-            assertThat(err.toString()).contains("<stdin>:4:3: error: class, interface");
+            assertThat(err.toString()).contains("<stdin>:4:2: error: class, interface");
 
         } finally {
             Locale.setDefault(backupLocale);
@@ -584,7 +584,7 @@ public void exitIfChangedLosesToParseError() throws Exception {
                 .isEqualTo(1);
         assertThat(main.format("-n", "--set-exit-if-changed", unformatted.toString(), broken.toString()))
                 .isEqualTo(2);
-        assertThat(err.toString()).contains("Broken.java:1:16: error: reached end of file");
+        assertThat(err.toString()).contains("Broken.java:1:15: error: reached end of file");
     }
 
     @Test
@@ -599,7 +599,7 @@ public void assumeFilename_error() throws Exception {
                 new PrintWriter(err, true),
                 new ByteArrayInputStream(joiner.join(input).getBytes(UTF_8)));
         assertThat(main.format("--assume-filename=Foo.java", "-")).isEqualTo(2);
-        assertThat(err.toString()).contains("Foo.java:1:15: error: class, interface");
+        assertThat(err.toString()).contains("Foo.java:1:14: error: class, interface");
     }
 
     @Test