diff --git a/packages/core/src/parameter/scanner.ts b/packages/core/src/parameter/scanner.ts
index daafe25..02fdd86 100644
--- a/packages/core/src/parameter/scanner.ts
+++ b/packages/core/src/parameter/scanner.ts
@@ -439,7 +439,7 @@ function findFlagsByArgument<CONTEXT extends CommandContext>(
     return [];
 }
 
-const FLAG_NAME_VALUE_PATTERN = /^--([a-z][a-z-]+)=(.+)$/i;
+const FLAG_NAME_VALUE_PATTERN = /^--([a-z][a-z-.\d_]+)=(.+)$/i;
 const ALIAS_VALUE_PATTERN = /^-([a-z])=(.+)$/i;
 
 /**
diff --git a/packages/core/tests/baselines/reference/parameter/flag/formatting.txt b/packages/core/tests/baselines/reference/parameter/flag/formatting.txt
index 8fdbad7..9887df5 100644
--- a/packages/core/tests/baselines/reference/parameter/flag/formatting.txt
+++ b/packages/core/tests/baselines/reference/parameter/flag/formatting.txt
@@ -44,6 +44,14 @@
 :::: formatDocumentationForFlagParameters / no flags
 -h --help  Print help information and exit
    --      All subsequent inputs should be interpreted as arguments
+:::: formatDocumentationForFlagParameters / parsed / flag with nonstandard character
+   --a.b.c_10  required parsed flag
+-h --help      Print help information and exit
+   --          All subsequent inputs should be interpreted as arguments
+:::: formatDocumentationForFlagParameters / parsed / multipart flag
+   --multi.part  required parsed flag
+-h --help        Print help information and exit
+   --            All subsequent inputs should be interpreted as arguments
 :::: formatDocumentationForFlagParameters / parsed / multiple parsed flags
    --requiredParsed                        required parsed flag
    --requiredParsedWithLongerName          required parsed flag with longer name
diff --git a/packages/core/tests/parameter/flag/formatting.spec.ts b/packages/core/tests/parameter/flag/formatting.spec.ts
index 3865c3a..8a79914 100644
--- a/packages/core/tests/parameter/flag/formatting.spec.ts
+++ b/packages/core/tests/parameter/flag/formatting.spec.ts
@@ -728,5 +728,55 @@ describe("formatDocumentationForFlagParameters", function () {
             // THEN
             compareToBaseline(this, StringArrayBaselineFormat, lines);
         });
+
+        it("multipart flag", function () {
+            // GIVEN
+            type Positional = [];
+            type Flags = {
+                readonly "multi.part": string;
+            };
+
+            const parameters: TypedCommandParameters<Flags, Positional, CommandContext> = {
+                flags: {
+                    "multi.part": {
+                        kind: "parsed",
+                        parse: String,
+                        brief: "required parsed flag",
+                    },
+                },
+                positional: { kind: "tuple", parameters: [] },
+            };
+
+            // WHEN
+            const lines = formatDocumentationForFlagParameters(parameters.flags, parameters.aliases ?? {}, defaultArgs);
+
+            // THEN
+            compareToBaseline(this, StringArrayBaselineFormat, lines);
+        });
+
+        it("flag with nonstandard character", function () {
+            // GIVEN
+            type Positional = [];
+            type Flags = {
+                readonly "a.b.c_10": string;
+            };
+
+            const parameters: TypedCommandParameters<Flags, Positional, CommandContext> = {
+                flags: {
+                    "a.b.c_10": {
+                        kind: "parsed",
+                        parse: String,
+                        brief: "required parsed flag",
+                    },
+                },
+                positional: { kind: "tuple", parameters: [] },
+            };
+
+            // WHEN
+            const lines = formatDocumentationForFlagParameters(parameters.flags, parameters.aliases ?? {}, defaultArgs);
+
+            // THEN
+            compareToBaseline(this, StringArrayBaselineFormat, lines);
+        });
     });
 });