diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4c80c558..897395a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 ## 9.0.1 (upcoming)
 
 - Ignore `\pgfmathsetmacro`, `\setmainfont`, and `\theoremstyle`
+- Fix accent commands such as `\O` in math mode resulting in diagnostics (fixes [vscode-ltex#216](https://github.com/valentjn/vscode-ltex/issues/216))
 
 ## 9.0.0 (January 3, 2021)
 
diff --git a/ltexls-core/src/main/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilder.java b/ltexls-core/src/main/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilder.java
index d6e190f5..db1b9931 100644
--- a/ltexls-core/src/main/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilder.java
+++ b/ltexls-core/src/main/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilder.java
@@ -561,21 +561,21 @@ public LatexAnnotatedTextBuilder addCode(String code) {
               popMode();
               addMarkup(command, generateDummy());
             } else if (command.equals("\\AA")) {
-              addMarkup(command, "\u00c5");
+              addMarkup(command, (isMathMode(this.curMode) ? "" : "\u00c5"));
             } else if (command.equals("\\O")) {
-              addMarkup(command, "\u00d8");
+              addMarkup(command, (isMathMode(this.curMode) ? "" : "\u00d8"));
             } else if (command.equals("\\aa")) {
-              addMarkup(command, "\u00e5");
+              addMarkup(command, (isMathMode(this.curMode) ? "" : "\u00e5"));
             } else if (command.equals("\\ss")) {
-              addMarkup(command, "\u00df");
+              addMarkup(command, (isMathMode(this.curMode) ? "" : "\u00df"));
             } else if (command.equals("\\o")) {
-              addMarkup(command, "\u00f8");
+              addMarkup(command, (isMathMode(this.curMode) ? "" : "\u00f8"));
             } else if (command.equals("\\`") || command.equals("\\'") || command.equals("\\^")
                   || command.equals("\\~") || command.equals("\\\"") || command.equals("\\=")
                   || command.equals("\\.")) {
               Matcher matcher = accentPattern1.matcher(code.substring(this.pos));
 
-              if (matcher.find()) {
+              if (!isMathMode(this.curMode) && matcher.find()) {
                 @Nullable String accentCommand = matcher.group(1);
                 @Nullable String letter = ((matcher.group(3) != null)
                     ? matcher.group(3) : matcher.group(5));
@@ -588,7 +588,7 @@ public LatexAnnotatedTextBuilder addCode(String code) {
             } else if (command.equals("\\c") || command.equals("\\r")) {
               Matcher matcher = accentPattern2.matcher(code.substring(this.pos));
 
-              if (matcher.find()) {
+              if (!isMathMode(this.curMode) && matcher.find()) {
                 @Nullable String accentCommand = matcher.group(1);
                 @Nullable String letter = ((matcher.group(3) != null)
                     ? matcher.group(3) : matcher.group(4));
diff --git a/ltexls-core/src/test/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilderTest.java b/ltexls-core/src/test/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilderTest.java
index 1b465932..f5aea00a 100644
--- a/ltexls-core/src/test/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilderTest.java
+++ b/ltexls-core/src/test/java/org/bsplines/ltexls/parsing/latex/LatexAnnotatedTextBuilderTest.java
@@ -223,6 +223,13 @@ public void testMathMode() {
         + "  a \\text{,~and} b.\n"
         + "\\end{equation*}\n",
         "This is a test: Dummy0,\u00a0and Dummy1. ");
+    assertPlainText(
+        "This is a test:\n"
+        + "\\begin{equation}\n"
+        + "    Gau\\ss{}: \\O(n^2).\n"
+        + "\\end{equation}\n"
+        + "This is another test: $Gau\\ss{}: \\O(n^2)$.\n",
+        "This is a test: Dummy0. This is another test: Dummy1. ");
     assertPlainText(
         "This is a test:\n"
         + "\\[\n"