diff --git a/src/core/jpg.js b/src/core/jpg.js
index 619cf5c35..d9c49fa70 100644
--- a/src/core/jpg.js
+++ b/src/core/jpg.js
@@ -991,8 +991,10 @@ var JpegImage = (function JpegImageClosure() {
             var components = [],
               component;
             for (i = 0; i < selectorsCount; i++) {
-              var componentIndex = frame.componentIds[data[offset++]];
+              const index = data[offset++];
+              var componentIndex = frame.componentIds[index];
               component = frame.components[componentIndex];
+              component.index = index;
               var tableSpec = data[offset++];
               component.huffmanTableDC = huffmanTablesDC[tableSpec >> 4];
               component.huffmanTableAC = huffmanTablesAC[tableSpec & 15];
@@ -1088,6 +1090,7 @@ var JpegImage = (function JpegImageClosure() {
         }
 
         this.components.push({
+          index: component.index,
           output: buildComponentData(frame, component),
           scaleX: component.h / frame.maxH,
           scaleY: component.v / frame.maxV,
@@ -1183,6 +1186,14 @@ var JpegImage = (function JpegImageClosure() {
           // dictionary has a 'ColorTransform' entry, explicitly set to `0`,
           // then the colours should *not* be transformed.
           return false;
+        } else if (
+          this.components[0].index === /* "R" = */ 0x52 &&
+          this.components[1].index === /* "G" = */ 0x47 &&
+          this.components[2].index === /* "B" = */ 0x42
+        ) {
+          // If the three components are indexed as RGB in ASCII
+          // then the colours should *not* be transformed.
+          return false;
         }
         return true;
       }
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index 680b5a66a..4d463ddc9 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -147,6 +147,7 @@
 !issue1055r.pdf
 !issue11713.pdf
 !issue1293r.pdf
+!issue11931.pdf
 !issue1655r.pdf
 !issue6541.pdf
 !issue2948.pdf
diff --git a/test/pdfs/issue11931.pdf b/test/pdfs/issue11931.pdf
new file mode 100644
index 000000000..787bb7bf0
Binary files /dev/null and b/test/pdfs/issue11931.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index cb3b99ea7..b0b29be84 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -4367,6 +4367,12 @@
        "type": "eq",
        "forms": true
     },
+    {  "id": "issue11931",
+       "file": "pdfs/issue11931.pdf",
+       "md5": "9ea233037992e1f10280420a49e72845",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "annotation-button-widget-annotations",
        "file": "pdfs/annotation-button-widget.pdf",
        "md5": "5cf23adfff84256d9cfe261bea96dade",