diff --git a/src/diff.c b/src/diff.c
index 971ef65..7e56641 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1824,8 +1824,14 @@
 		dp->df_count[idx_new] = hunk->count_new - off;
 	    }
 	    else
+	    {
 		// second overlap of new block with existing block
 		dp->df_count[idx_new] += hunk->count_new;
+		if ((dp->df_lnum[idx_new] + dp->df_count[idx_new] - 1)
+			> curtab->tp_diffbuf[idx_new]->b_ml.ml_line_count)
+		    dp->df_count[idx_new] = curtab->tp_diffbuf[idx_new]->b_ml.ml_line_count
+			- dp->df_lnum[idx_new] + 1;
+	    }
 
 	    // Adjust the size of the block to include all the lines to the
 	    // end of the existing block or the new diff, whatever ends last.
@@ -1835,6 +1841,10 @@
 	    {
 		// new change ends in existing block, adjust the end
 		dp->df_count[idx_new] += -off;
+		if ((dp->df_lnum[idx_new] + dp->df_count[idx_new] - 1)
+			> curtab->tp_diffbuf[idx_new]->b_ml.ml_line_count)
+		    dp->df_count[idx_new] = curtab->tp_diffbuf[idx_new]->b_ml.ml_line_count
+			- dp->df_lnum[idx_new] + 1;
 		off = 0;
 	    }
 	    for (i = idx_orig; i < idx_new; ++i)
diff --git a/src/testdir/dumps/Test_diff_overlapped_3.38.dump b/src/testdir/dumps/Test_diff_overlapped_3.38.dump
new file mode 100644
index 0000000..6271815
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_overlapped_3.38.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1|a+2#0000000#ff404010| +0&#ffd7ff255@21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|d+2#0000000#ff404010| +0&#ffd7ff255@20||+1&#ffffff0| +0#0000e05#a8a8a8255@1|b+2#0000000#ff404010| +0&#ffd7ff255@20
+| +0#0000e05#a8a8a8255@1|b+2#0000000#ff404010| +0&#ffd7ff255@21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|e+2#0000000#ff404010| +0&#ffd7ff255@20||+1&#ffffff0| +0#0000e05#a8a8a8255@1|f+2#0000000#ff404010| +0&#ffd7ff255@20
+| +0#0000e05#a8a8a8255@1|c+0#0000000#5fd7ff255| @21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@21||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@21
+|~+0&#ffffff0| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|X+3#0000000&|d|i|f|i|l|e|1| @4|1|,|1| @5|A|l@1| |X+1&&|d|i|f|i|l|e|2| @3|1|,|1| @5|A|l@1| |X|d|i|f|i|l|e|3| @3|1|,|1| @5|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/dumps/Test_diff_overlapped_3.39.dump b/src/testdir/dumps/Test_diff_overlapped_3.39.dump
new file mode 100644
index 0000000..9f1a5cd
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_overlapped_3.39.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1|a+2#0000000#ff404010| +0&#ffd7ff255@21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|d+2#0000000#ff404010| +0&#ffd7ff255@20||+1&#ffffff0| +0#0000e05#a8a8a8255@1|b+2#0000000#ff404010| +0&#ffd7ff255@20
+| +0#0000e05#a8a8a8255@1|b+2#0000000#ff404010| +0&#ffd7ff255@21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|e+2#0000000#ff404010| +0&#ffd7ff255@20||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@21
+| +0#0000e05#a8a8a8255@1|c+0#0000000#5fd7ff255| @21||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@21||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@21
+|~+0&#ffffff0| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|~| @23||+1#0000000&|~+0#4040ff13&| @22||+1#0000000&|~+0#4040ff13&| @22
+|X+3#0000000&|d|i|f|i|l|e|1| @4|1|,|1| @5|A|l@1| |X+1&&|d|i|f|i|l|e|2| @3|1|,|1| @5|A|l@1| |X|d|i|f|i|l|e|3| @3|1|,|1| @5|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 1c7233e..8939bb8 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
Binary files differ
diff --git a/src/version.c b/src/version.c
index 39c0aa6..51635c7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1018,
+/**/
     1017,
 /**/
     1016,