diff --git a/libs/core-functions-lib/__tests__/strings.test.ts b/libs/core-functions-lib/__tests__/strings.test.ts
index 0513c4ba0..6ee5e3361 100644
--- a/libs/core-functions-lib/__tests__/strings.test.ts
+++ b/libs/core-functions-lib/__tests__/strings.test.ts
@@ -59,6 +59,13 @@ const dataExtra: Record<string, string> = {
   "$Camel##Case#": "$camel##case#",
 };
 
+const dataDigits: Record<string, string> = {
+  // underscore must be inserted between a digit and a following capital letter
+  field1Name: "field1_name",
+  address2Line: "address2_line",
+  plan9FromOuterSpace: "plan9_from_outer_space",
+};
+
 test("test idToSnakeCaseFast", async () => {
   for (const [value, expected] of Object.entries(data)) {
     const res = idToSnakeCaseFast(value);
@@ -79,3 +86,16 @@ test("test idToSnakeCaseRegex", async () => {
     expect(res).toEqual(expected);
   }
 });
+
+test("test idToSnakeCaseFast with digits", async () => {
+  for (const [value, expected] of Object.entries(dataDigits)) {
+    const res = idToSnakeCaseFast(value);
+    expect(res).toEqual(expected);
+  }
+});
+
+test("test idToSnakeCaseFast matches idToSnakeCaseRegex on digit boundaries", async () => {
+  for (const value of Object.keys(dataDigits)) {
+    expect(idToSnakeCaseFast(value)).toEqual(idToSnakeCaseRegex(value));
+  }
+});
diff --git a/libs/functions/src/lib/strings.ts b/libs/functions/src/lib/strings.ts
index bd41ef283..0f5325d05 100644
--- a/libs/functions/src/lib/strings.ts
+++ b/libs/functions/src/lib/strings.ts
@@ -22,8 +22,8 @@ export function idToSnakeCaseFast(id: string) {
       concatIndex = i + 1;
     }
     // needUnderscore is used in case next char is a capital latin letter
-    // we add underscore only between latin letters
-    needUnderscore = (c >= aCode && c <= zCode) || (c >= ACode && c <= ZCode);
+    // we add underscore after a latin letter or a digit
+    needUnderscore = (c >= aCode && c <= zCode) || (c >= ACode && c <= ZCode) || (c >= zeroCode && c <= nineCode);
   }
   if (concatIndex == 0) {
     return id;