diff --git a/src/source-map/build-source-map.ts b/src/source-map/build-source-map.ts
index a6c7638..892575e 100644
--- a/src/source-map/build-source-map.ts
+++ b/src/source-map/build-source-map.ts
@@ -24,6 +24,7 @@ import type {
   MarkdownSourceMap,
   MarkdownSourceMapSegment,
   ParsedMarkdownDocument,
+  SourceSpan,
 } from './types';
 
 // Use the exact same parser extensions as `parseMd` so the AST (and therefore
@@ -292,11 +293,6 @@ function buildUrlSegments(
   return value === node.url ? { segments } : undefined;
 }
 
-interface SourceSpan {
-  start: number
-  end: number
-}
-
 /**
  * Find the segment covering `valueIndex`, or undefined.
  *
diff --git a/src/source-map/code-segments.ts b/src/source-map/code-segments.ts
index 8a67221..74db072 100644
--- a/src/source-map/code-segments.ts
+++ b/src/source-map/code-segments.ts
@@ -1,16 +1,11 @@
 import type { ParsedPosition } from '../types';
-import type { MarkdownSourceMapSegment } from './types';
+import type { MarkdownSourceMapSegment, SourceSpan } from './types';
 
 interface CodeSegments {
   segments: MarkdownSourceMapSegment[]
   emptyOffset?: number
 }
 
-interface SourceSpan {
-  start: number
-  end: number
-}
-
 function lineEnd(md: string, start: number, limit: number): number {
   let offset = start;
   while (offset < limit) {
diff --git a/src/source-map/recording-extension.ts b/src/source-map/recording-extension.ts
index e97fc07..e5edfeb 100644
--- a/src/source-map/recording-extension.ts
+++ b/src/source-map/recording-extension.ts
@@ -1,12 +1,7 @@
 import { decodeNamedCharacterReference } from 'decode-named-character-reference';
 import { decodeNumericCharacterReference } from 'micromark-util-decode-numeric-character-reference';
 import type { ParsedPoint } from '../types';
-import type { MarkdownSourceMapSegment } from './types';
-
-interface SourceSpan {
-  start: number
-  end: number
-}
+import type { MarkdownSourceMapSegment, SourceSpan } from './types';
 
 interface RecordingState {
   segments: WeakMap<object, MarkdownSourceMapSegment[]>
diff --git a/src/source-map/types.ts b/src/source-map/types.ts
index 600bc3d..733a047 100644
--- a/src/source-map/types.ts
+++ b/src/source-map/types.ts
@@ -8,6 +8,16 @@ import type {
   ParsedPosition,
 } from '../types';
 
+/**
+ * An absolute half-open interval in the Markdown source.
+ *
+ * @internal
+ */
+export interface SourceSpan {
+  start: number
+  end: number
+}
+
 /**
  * The kind of transformation the parser applied to turn a slice of the raw
  * Markdown source into the corresponding slice of a node's normalized value.