diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index c5baf23ee9fc2..5132cc830d0cf 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -4261,7 +4261,8 @@ class PartialEvaluator {
             this.idFactory,
             this.options.standardFontDataUrl,
             baseFontName,
-            standardFontName
+            standardFontName,
+            type
           );
         }
 
@@ -4381,7 +4382,8 @@ class PartialEvaluator {
           this.idFactory,
           this.options.standardFontDataUrl,
           fontName.name,
-          standardFontName
+          standardFontName,
+          type
         );
       }
     }
diff --git a/src/core/font_substitutions.js b/src/core/font_substitutions.js
index ec973b84919ff..426e6b47e3034 100644
--- a/src/core/font_substitutions.js
+++ b/src/core/font_substitutions.js
@@ -456,6 +456,7 @@ function generateFont(
  * @param {String} baseFontName The font name to be substituted.
  * @param {String|undefined} standardFontName The standard font name to use
  *   if the base font is not available.
+ * @param {String} type The font type.
  * @returns an Object with the CSS, the loaded name, the src and the style.
  */
 function getFontSubstitution(
@@ -463,12 +464,21 @@ function getFontSubstitution(
   idFactory,
   localFontPath,
   baseFontName,
-  standardFontName
+  standardFontName,
+  type
 ) {
   if (baseFontName.startsWith("InvalidPDFjsFont_")) {
     return null;
   }
 
+  if (
+    (type === "TrueType" || type === "Type1") &&
+    /^[A-Z]{6}\+/.test(baseFontName)
+  ) {
+    // When the font is a subset, we need to remove the prefix (see 9.6.4).
+    baseFontName = baseFontName.slice(7);
+  }
+
   // It's possible to have a font name with spaces, commas or dashes, hence we
   // just replace them by a dash.
   baseFontName = normalizeFontName(baseFontName);
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index d8515d1c73565..057c3475869f1 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -641,3 +641,4 @@
 !issue17871_bottom_right.pdf
 !issue17871_top_right.pdf
 !bug1889122.pdf
+!issue17929.pdf
diff --git a/test/pdfs/issue17929.pdf b/test/pdfs/issue17929.pdf
new file mode 100755
index 0000000000000..e062143d095a2
Binary files /dev/null and b/test/pdfs/issue17929.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 85fb66cbe90f6..aa53c3e17df95 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -9833,5 +9833,12 @@
     "firstPage": 1,
     "lastPage": 1,
     "type": "eq"
+  },
+  {
+    "id": "issue17929",
+    "file": "pdfs/issue17929.pdf",
+    "md5": "2f5686f77f73fb99037f5c2c7e48ce53",
+    "rounds": 1,
+    "type": "eq"
   }
 ]
diff --git a/test/unit/font_substitutions_spec.js b/test/unit/font_substitutions_spec.js
index 8b7edd86d0a9a..bad2b76b40c1a 100644
--- a/test/unit/font_substitutions_spec.js
+++ b/test/unit/font_substitutions_spec.js
@@ -27,7 +27,32 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
+    );
+    expect(fontSubstitution).toEqual(
+      jasmine.objectContaining({
+        guessFallback: true,
+        baseFontName: "Foo",
+        src: "local(Foo)",
+        style: {
+          style: "normal",
+          weight: "normal",
+        },
+      })
+    );
+    expect(fontSubstitution.css).toMatch(/^"Foo",g_d(\d+)_sf(\d+)$/);
+  });
+
+  it("should substitute an unknown font subset", () => {
+    const fontName = "ABCDEF+Foo";
+    const fontSubstitution = getFontSubstitution(
+      new Map(),
+      idFactory,
+      localFontPath,
+      fontName,
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -50,7 +75,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -73,7 +99,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -96,7 +123,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -119,7 +147,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      "Helvetica"
+      "Helvetica",
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -150,7 +179,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      "Helvetica-Oblique"
+      "Helvetica-Oblique",
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -183,7 +213,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      "Helvetica-Bold"
+      "Helvetica-Bold",
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -215,7 +246,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      "Helvetica-BoldOblique"
+      "Helvetica-BoldOblique",
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -250,7 +282,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -283,7 +316,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -318,7 +352,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({
@@ -353,7 +388,8 @@ describe("getFontSubstitution", function () {
       idFactory,
       localFontPath,
       fontName,
-      undefined
+      undefined,
+      "TrueType"
     );
     expect(fontSubstitution).toEqual(
       jasmine.objectContaining({