diff --git a/src/Expr.cc b/src/Expr.cc
index 907cfc904c..2b55184945 100644
--- a/src/Expr.cc
+++ b/src/Expr.cc
@@ -3037,6 +3037,16 @@ Val* IndexExpr::Eval(Frame* f) const
 	return result;
 	}
 
+static int get_slice_index(int idx, int len)
+	{
+	if ( abs(idx) > len )
+		idx = idx > 0 ? len : 0;  // Clamp maximum positive/negative indices.
+	else if ( idx < 0 )
+		idx += len;  // Map to a positive index.
+
+	return idx;
+	}
+
 Val* IndexExpr::Fold(Val* v1, Val* v2) const
 	{
 	if ( IsError() )
@@ -3058,16 +3068,30 @@ Val* IndexExpr::Fold(Val* v1, Val* v2) const
 		const ListVal* lv = v2->AsListVal();
 		const BroString* s = v1->AsString();
 		int len = s->Len();
-		bro_int_t first = lv->Index(0)->AsInt();
-		bro_int_t last = lv->Length() > 1 ? lv->Index(1)->AsInt() : first;
+		BroString* substring = 0;
 
-		if ( first < 0 )
-			first += len;
+		if ( lv->Length() == 1 )
+			{
+			bro_int_t idx = lv->Index(0)->AsInt();
 
-		if ( last < 0 )
-			last += len;
+			if ( idx < 0 )
+				idx += len;
+
+			// Out-of-range index will return null pointer.
+			substring = s->GetSubstring(idx, 1);
+			}
+		else
+			{
+			bro_int_t first = get_slice_index(lv->Index(0)->AsInt(), len);
+			bro_int_t last = get_slice_index(lv->Index(1)->AsInt(), len);
+			int substring_len = last - first;
+
+			if ( substring_len < 0 )
+				substring = 0;
+			else
+				substring = s->GetSubstring(first, substring_len);
+			}
 
-		BroString* substring = s->GetSubstring(first, last - first + 1);
 		return new StringVal(substring ? substring : new BroString(""));
 		}
 
diff --git a/testing/btest/Baseline/language.string-indexing/out b/testing/btest/Baseline/language.string-indexing/out
index 3359187d4c..99464302ed 100644
--- a/testing/btest/Baseline/language.string-indexing/out
+++ b/testing/btest/Baseline/language.string-indexing/out
@@ -1,13 +1,85 @@
 1
-12
-123456
+1
+12345
 0123456789
 8
-789
-9
-9
-9
+78
 
 
+
+
+0123456789
 2
 1
+word[-100] = 
+word[-7] = 
+word[-6] = 
+word[-5] = H
+word[-4] = e
+word[-3] = l
+word[-2] = p
+word[-1] = A
+word[0] = H
+word[1] = e
+word[2] = l
+word[3] = p
+word[4] = A
+word[5] = 
+word[6] = 
+word[7] = 
+word[100] = 
+
+A
+1234
+123
+12
+1
+
+
+
+
+
+
+B
+
+
+
+
+
+C
+
+0123
+
+01
+012345
+
+D
+
+
+4
+
+
+45
+
+E
+
+01234
+
+01
+012345
+
+F
+
+234
+
+
+23
+2345
+
+F
+
+
+
+
+
+
diff --git a/testing/btest/language/string-indexing.bro b/testing/btest/language/string-indexing.bro
index f991b3c5fa..bff37f6bec 100644
--- a/testing/btest/language/string-indexing.bro
+++ b/testing/btest/language/string-indexing.bro
@@ -1,7 +1,10 @@
 # @TEST-EXEC: bro -b %INPUT >out
 # @TEST-EXEC: btest-diff out
 
+local word = "HelpA";
 local s = "0123456789";
+local indices = vector(-100, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 100);
+
 print s[1];
 print s[1:2];
 print s[1:6];
@@ -15,3 +18,77 @@ print s[20:23];
 print s[-20:23];
 print s[0:5][2];
 print s[0:5][1:3][0];
+
+s = "012345";
+
+for ( i in indices )
+	print fmt("word[%s] = %s", indices[i], word[indices[i]]);
+
+print "";
+
+print "A";
+print s[1:-1];
+print s[1:-2];
+print s[1:-3];
+print s[1:-4];
+print s[1:-5];
+print s[1:-6];
+print s[1:-7];
+print s[1:-8];
+print s[1:-9];
+
+print "";
+
+print "B";
+print s[-1:-1];
+print s[-1:-2];
+print s[-1:-3];
+print s[-1:-4];
+
+print "";
+
+print "C";
+print s[-100:-99];
+print s[-100:-2];
+print s[-100:0];
+print s[-100:2];
+print s[-100:100];
+
+print "";
+
+print "D";;
+print s[-2:-99];
+print s[-2:-3];
+print s[-2:-1];
+print s[-2:0];
+print s[-2:2];
+print s[-2:100];
+
+print "";
+
+print "E";;
+print s[0:-100];
+print s[0:-1];
+print s[0:0];
+print s[0:2];
+print s[0:100];
+
+print "";
+
+print "F";;
+print s[2:-100];
+print s[2:-1];
+print s[2:0];
+print s[2:1];
+print s[2:4];
+print s[2:100];
+
+print "";
+
+print "F";;
+print s[100:-100];
+print s[100:-1];
+print s[100:0];
+print s[100:1];
+print s[100:4];
+print s[100:100];
diff --git a/testing/scripts/file-analysis-test.bro b/testing/scripts/file-analysis-test.bro
index d84fadae5c..957218b48f 100644
--- a/testing/scripts/file-analysis-test.bro
+++ b/testing/scripts/file-analysis-test.bro
@@ -60,7 +60,7 @@ event file_new(f: fa_file)
 	if ( f?$bof_buffer )
 		{
 		print "FILE_BOF_BUFFER";
-		print f$bof_buffer[0:10];
+		print f$bof_buffer[0:11];
 		}
 
 	if ( f?$mime_type )