diff --git a/modules/imgcodecs/src/grfmt_pam.cpp b/modules/imgcodecs/src/grfmt_pam.cpp
index efae09f033..abc48cd1ad 100644
--- a/modules/imgcodecs/src/grfmt_pam.cpp
+++ b/modules/imgcodecs/src/grfmt_pam.cpp
@@ -175,28 +175,28 @@ rgb_convert (void *src, void *target, int width, int target_channels, int target
  */
 
 static void
-basic_conversion (void *src, const struct channel_layout *layout, int src_sampe_size,
+basic_conversion (void *src, const struct channel_layout *layout, int src_sample_size,
     int src_width, void *target, int target_channels, int target_depth, bool use_rgb)
 {
     switch (target_depth) {
         case CV_8U:
         {
             uchar *d = (uchar *)target, *s = (uchar *)src,
-                *end = ((uchar *)src) + src_width;
+                *end = ((uchar *)src) + src_width * src_sample_size;
             switch (target_channels) {
                 case 1:
-                    for( ; s < end; d += 3, s += src_sampe_size )
-                        d[0] = d[1] = d[2] = s[layout->graychan];
+                    for( ; s < end; d += 1, s += src_sample_size )
+                        d[0] = s[layout->graychan];
                     break;
                 case 3:
                     if (use_rgb)
-                        for( ; s < end; d += 3, s += src_sampe_size ) {
+                        for( ; s < end; d += 3, s += src_sample_size ) {
                             d[0] = s[layout->rchan];
                             d[1] = s[layout->gchan];
                             d[2] = s[layout->bchan];
                         }
                     else
-                        for( ; s < end; d += 3, s += src_sampe_size ) {
+                        for( ; s < end; d += 3, s += src_sample_size ) {
                             d[0] = s[layout->bchan];
                             d[1] = s[layout->gchan];
                             d[2] = s[layout->rchan];
@@ -210,21 +210,21 @@ basic_conversion (void *src, const struct channel_layout *layout, int src_sampe_
         case CV_16U:
         {
             ushort *d = (ushort *)target, *s = (ushort *)src,
-                *end = ((ushort *)src) + src_width;
+                *end = ((ushort *)src) + src_width * src_sample_size;
             switch (target_channels) {
                 case 1:
-                    for( ; s < end; d += 3, s += src_sampe_size )
-                        d[0] = d[1] = d[2] = s[layout->graychan];
+                    for( ; s < end; d += 1, s += src_sample_size )
+                        d[0] = s[layout->graychan];
                     break;
                 case 3:
                     if (use_rgb)
-                        for( ; s < end; d += 3, s += src_sampe_size ) {
+                        for( ; s < end; d += 3, s += src_sample_size ) {
                             d[0] = s[layout->rchan];
                             d[1] = s[layout->gchan];
                             d[2] = s[layout->bchan];
                         }
                     else
-                        for( ; s < end; d += 3, s += src_sampe_size ) {
+                        for( ; s < end; d += 3, s += src_sample_size ) {
                             d[0] = s[layout->bchan];
                             d[1] = s[layout->gchan];
                             d[2] = s[layout->rchan];
diff --git a/modules/imgcodecs/test/test_grfmt.cpp b/modules/imgcodecs/test/test_grfmt.cpp
index 87d8780442..bc31cc3c6a 100644
--- a/modules/imgcodecs/test/test_grfmt.cpp
+++ b/modules/imgcodecs/test/test_grfmt.cpp
@@ -564,6 +564,37 @@ TEST(Imgcodecs_Pam, read_write)
     remove(writefile.c_str());
     remove(writefile_no_param.c_str());
 }
+
+// Regression test: a 2-channel (GRAYSCALE_ALPHA) PAM decoded as single channel
+// used to overflow the output row in basic_conversion() (3 bytes written per
+// source pixel into a 1-channel row). Verify it decodes safely and correctly.
+TEST(Imgcodecs_Pam, decode_graya_as_gray)
+{
+    const int width = 9, height = 3;  // odd width to expose off-by-row overflow
+    std::string header = cv::format(
+        "P7\nWIDTH %d\nHEIGHT %d\nDEPTH 2\nMAXVAL 255\n"
+        "TUPLTYPE GRAYSCALE_ALPHA\nENDHDR\n", width, height);
+
+    std::vector<uchar> buf(header.begin(), header.end());
+    Mat gray_ref(height, width, CV_8UC1);
+    for (int y = 0; y < height; y++)
+        for (int x = 0; x < width; x++)
+        {
+            uchar gray  = (uchar)((y * width + x) * 7 + 1);
+            uchar alpha = (uchar)(255 - gray);
+            gray_ref.at<uchar>(y, x) = gray;
+            buf.push_back(gray);   // channel 0: gray
+            buf.push_back(alpha);  // channel 1: alpha (must be ignored)
+        }
+
+    Mat decoded;
+    ASSERT_NO_THROW(decoded = imdecode(buf, IMREAD_GRAYSCALE));
+    ASSERT_FALSE(decoded.empty());
+    EXPECT_EQ(width, decoded.cols);
+    EXPECT_EQ(height, decoded.rows);
+    EXPECT_EQ(1, decoded.channels());
+    EXPECT_EQ(0, cvtest::norm(gray_ref, decoded, NORM_INF));
+}
 #endif
 
 #ifdef HAVE_IMGCODEC_PFM