diff --git a/packages/babel-core/src/transformation/normalize-file.js b/packages/babel-core/src/transformation/normalize-file.js
index 6326dd385e66..cc7db60a5478 100644
--- a/packages/babel-core/src/transformation/normalize-file.js
+++ b/packages/babel-core/src/transformation/normalize-file.js
@@ -65,7 +65,8 @@ export default function normalizeFile(
       if (typeof options.filename === "string" && lastComment) {
         try {
           inputMap = convertSourceMap.fromMapFileComment(
-            lastComment,
+            // fromMapFileComment requires the whole comment block
+            `//${lastComment}`,
             path.dirname(options.filename),
           );
         } catch (err) {
@@ -156,7 +157,7 @@ function parser(
 
 // eslint-disable-next-line max-len
 const INLINE_SOURCEMAP_REGEX = /^[@#]\s+sourceMappingURL=data:(?:application|text)\/json;(?:charset[:=]\S+?;)?base64,(?:.*)$/;
-const EXTERNAL_SOURCEMAP_REGEX = /^[@#][ \t]+sourceMappingURL=([^\s'"`]+?)[ \t]*$/;
+const EXTERNAL_SOURCEMAP_REGEX = /^[@#][ \t]+sourceMappingURL=(?:[^\s'"`]+?)[ \t]*$/;
 
 function extractCommentsFromList(regex, comments, lastComment) {
   if (comments) {
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js
new file mode 100644
index 000000000000..f7250b67d0b4
--- /dev/null
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js
@@ -0,0 +1,5 @@
+var foo = function () {
+  return 4;
+};
+
+//# sourceMappingURL=input.js.map
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js.map b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js.map
new file mode 100644
index 000000000000..cb88961ebdc0
--- /dev/null
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/input.js.map
@@ -0,0 +1 @@
+{"version":3,"sources":["original.js"],"names":[],"mappings":"AAAA,UAAU,Y;SAAM,C;CAAC","sourcesContent":["var foo = () => 4;"]}
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/options.json b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/options.json
new file mode 100644
index 000000000000..0e6084f210d8
--- /dev/null
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/options.json
@@ -0,0 +1,3 @@
+{
+  "inputSourceMap": true
+}
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/output.js b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/output.js
new file mode 100644
index 000000000000..cf3efeceb306
--- /dev/null
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/output.js
@@ -0,0 +1,3 @@
+var foo = function () {
+  return 4;
+};
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/source-map.json b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/source-map.json
new file mode 100644
index 000000000000..63c01db5fede
--- /dev/null
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-external/source-map.json
@@ -0,0 +1,7 @@
+{
+  "mappings": "AAAA,IAAA,GAAA,GAAU,Y;SAAM,C;AAAC,CAAjB",
+  "names": [],
+  "sources": ["original.js"],
+  "sourcesContent": ["var foo = () => 4;"],
+  "version": 3
+}