diff --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -418,7 +418,11 @@
   if (!config->copyRelocs || (type != SHT_RELA && type != SHT_REL))
     return;
 
-  if (isa<SyntheticSection>(first))
+  // Skip if 'first' is synthetic, i.e. not a section created by --emit-relocs.
+  // Normally 'type' was changed by 'first' so 'first' should be non-null.
+  // However, if the output section is .rela.dyn, 'type' can be set by the empty
+  // synthetic .rela.plt and first can be null.
+  if (!first || isa<SyntheticSection>(first))
     return;
 
   link = in.symTab->getParent()->sectionIndex;
diff --git a/lld/test/ELF/linkerscript/emit-relocs-rela-dyn.s b/lld/test/ELF/linkerscript/emit-relocs-rela-dyn.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/linkerscript/emit-relocs-rela-dyn.s
@@ -0,0 +1,12 @@
+# REQUIRES: x86
+## PR48357: If .rela.dyn appears as an output section description, its type may
+## be SHT_RELA (due to the empty synthetic .rela.plt) while there is no input
+## section. The empty .rela.dyn may be retained due to a reference. Don't crash.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 /dev/null -o %t.o
+# RUN: ld.lld -shared --emit-relocs -T %s %t.o -o /dev/null
+
+SECTIONS {
+  .rela.dyn : { *(.rela*) }
+  __rela_offset = ABSOLUTE(ADDR(.rela.dyn));
+}