diff --git a/Makefile b/Makefile
index 4443718c8..968e62fac 100644
--- a/Makefile
+++ b/Makefile
@@ -176,7 +176,7 @@ ifeq ($(OS), Haiku)
 CXXFLAGS += -D_DEFAULT_SOURCE
 endif
 
-YOSYS_VER := 0.54+15
+YOSYS_VER := 0.54+17
 YOSYS_MAJOR := $(shell echo $(YOSYS_VER) | cut -d'.' -f1)
 YOSYS_MINOR := $(shell echo $(YOSYS_VER) | cut -d'.' -f2)
 YOSYS_COMMIT := $(shell echo $(YOSYS_VER) | cut -d'.' -f3)
diff --git a/frontends/verilog/verilog_lexer.l b/frontends/verilog/verilog_lexer.l
index 8148748d8..40162b8d3 100644
--- a/frontends/verilog/verilog_lexer.l
+++ b/frontends/verilog/verilog_lexer.l
@@ -336,7 +336,7 @@ TIME_SCALE_SUFFIX [munpf]?s
 }
 
 \"		{ BEGIN(STRING); }
-<STRING>([^\"]|\\.)+	{ yymore(); real_location = old_location; }
+<STRING>([^\\"]|\\.)+	{ yymore(); real_location = old_location; }
 <STRING>\"	{
 	BEGIN(0);
 	char *yystr = strdup(yytext);
diff --git a/frontends/verilog/verilog_parser.y b/frontends/verilog/verilog_parser.y
index 7e53005f3..17edc357d 100644
--- a/frontends/verilog/verilog_parser.y
+++ b/frontends/verilog/verilog_parser.y
@@ -2874,6 +2874,7 @@ behavioral_stmt:
 	} |
 	if_attr TOK_IF '(' expr ')' {
 		AstNode *node = 0;
+		AstNode *block = new AstNode(AST_BLOCK);
 		AstNode *context = ast_stack.back();
 		if (context && context->type == AST_BLOCK && context->get_bool_attribute(ID::promoted_if)) {
 			AstNode *outer = ast_stack[ast_stack.size() - 2];
@@ -2882,8 +2883,10 @@ behavioral_stmt:
 				// parallel "else if": append condition to outer "if"
 				node = outer;
 				log_assert (node->children.size());
+				ast_stack.pop_back();
 				delete node->children.back();
 				node->children.pop_back();
+				ast_stack.push_back(block);
 			} else if (outer->get_bool_attribute(ID::full_case))
 				(*$1)[ID::full_case] = AstNode::mkconst_int(1, false);
 		}
@@ -2894,8 +2897,8 @@ behavioral_stmt:
 			append_attr(node, $1);
 			ast_stack.back()->children.push_back(node);
 			node->children.push_back(node->get_bool_attribute(ID::parallel_case) ? AstNode::mkconst_int(1, false, 1) : expr);
-		}
-		AstNode *block = new AstNode(AST_BLOCK);
+		} else
+			free_attr($1);
 		AstNode *cond = new AstNode(AST_COND, node->get_bool_attribute(ID::parallel_case) ? expr : AstNode::mkconst_int(1, false, 1), block);
 		SET_AST_NODE_LOC(cond, @4, @4);
 		node->children.push_back(cond);
diff --git a/passes/opt/opt_dff.cc b/passes/opt/opt_dff.cc
index c4c01ea66..07d5bc289 100644
--- a/passes/opt/opt_dff.cc
+++ b/passes/opt/opt_dff.cc
@@ -760,7 +760,11 @@ struct OptDffWorker
 		ModWalker modwalker(module->design, module);
 		QuickConeSat qcsat(modwalker);
 
-		// Run as a separate sub-pass, so that we don't mutate (non-FF) cells under ModWalker.
+		// Defer mutating cells by removing them/emiting new flip flops so that
+		// cell references in modwalker are not invalidated
+		std::vector<RTLIL::Cell*> cells_to_remove;
+		std::vector<FfData> ffs_to_emit;
+
 		bool did_something = false;
 		for (auto cell : module->selected_cells()) {
 			if (!RTLIL::builtin_ff_cell_types().count(cell->type))
@@ -852,16 +856,20 @@ struct OptDffWorker
 					if (!removed_sigbits.count(i))
 						keep_bits.push_back(i);
 				if (keep_bits.empty()) {
-					module->remove(cell);
+					cells_to_remove.emplace_back(cell);
 					did_something = true;
 					continue;
 				}
 				ff = ff.slice(keep_bits);
 				ff.cell = cell;
-				ff.emit();
+				ffs_to_emit.emplace_back(ff);
 				did_something = true;
 			}
 		}
+		for (auto* cell : cells_to_remove)
+			module->remove(cell);
+		for (auto& ff : ffs_to_emit)
+			ff.emit();
 		return did_something;
 	}
 };
diff --git a/tests/opt/bug5164.ys b/tests/opt/bug5164.ys
new file mode 100644
index 000000000..4ee71fe45
--- /dev/null
+++ b/tests/opt/bug5164.ys
@@ -0,0 +1,60 @@
+read_rtlil <<EOT
+module \module137
+  wire input 1 \clk
+  wire width 1 output 1 \qa
+  wire width 1 \qb
+  cell $dff \dffa
+    parameter \CLK_POLARITY 1
+    parameter \WIDTH 1
+    connect \CLK \clk
+    connect \D \qb
+    connect \Q \qa
+  end
+  cell $dff \dffb
+    parameter \CLK_POLARITY 1
+    parameter \WIDTH 1
+    connect \CLK \clk
+    connect \D 1'x
+    connect \Q \qb
+  end
+end
+EOT
+equiv_opt -assert opt_dff -sat
+
+design -reset
+
+read_rtlil <<EOT
+module \module137
+  wire output 1 width 9 $2\reg204[8:0]
+  wire input 1 \clk
+  wire width 9 $auto$wreduce.cc:514:run$19340
+  wire width 9 $auto$wreduce.cc:514:run$19341
+  wire width 15 \dffout
+  attribute \init 9'000000000
+  wire width 9 \reg204
+  cell $dff $auto$ff.cc:266:slice$26225
+    parameter \CLK_POLARITY 1
+    parameter \WIDTH 15
+    connect \CLK \clk
+    connect \D { 9'x \reg204 [8:3] }
+    connect \Q \dffout
+  end
+  cell $dff $auto$ff.cc:266:slice$26292
+    parameter \CLK_POLARITY 1
+    parameter \WIDTH 9
+    connect \CLK \clk
+    connect \D $2\reg204[8:0]
+    connect \Q \reg204
+  end
+  cell $mux $procmux$4510
+    parameter \WIDTH 9
+    connect \A 9'x
+    connect \B 9'x
+    connect \S 1'x
+    connect \Y $auto$wreduce.cc:514:run$19340
+  end
+  connect $2\reg204[8:0] $auto$wreduce.cc:514:run$19340
+  connect $auto$wreduce.cc:514:run$19341 [8:3] 6'000000
+end
+EOT
+equiv_opt -assert opt_dff -sat
diff --git a/tests/verilog/bug5160.v b/tests/verilog/bug5160.v
new file mode 100644
index 000000000..5b141a360
--- /dev/null
+++ b/tests/verilog/bug5160.v
@@ -0,0 +1,5 @@
+// Regression test for bug mentioned in #5160:
+// https://github.com/YosysHQ/yosys/pull/5160#issuecomment-2983643084
+module top;
+    initial $display( "\\" );
+endmodule