diff --git a/llvm/docs/CommandGuide/llvm-addr2line.rst b/llvm/docs/CommandGuide/llvm-addr2line.rst
--- a/llvm/docs/CommandGuide/llvm-addr2line.rst
+++ b/llvm/docs/CommandGuide/llvm-addr2line.rst
@@ -17,6 +17,11 @@
 
 Here are some of those differences:
 
+-  ``llvm-addr2line`` interprets all addresses as hexadecimal and ignores an
+   optional ``0x`` prefix, whereas ``llvm-symbolizer`` attempts to determine
+   the base from the literal's prefix and defaults to decimal if there is no
+   prefix.
+
 -  ``llvm-addr2line`` defaults not to print function names. Use `-f`_ to enable
    that.
 
diff --git a/llvm/test/lit.cfg.py b/llvm/test/lit.cfg.py
--- a/llvm/test/lit.cfg.py
+++ b/llvm/test/lit.cfg.py
@@ -146,10 +146,10 @@
 # FIXME: Why do we have both `lli` and `%lli` that do slightly different things?
 tools.extend([
     'dsymutil', 'lli', 'lli-child-target', 'llvm-ar', 'llvm-as',
-    'llvm-bcanalyzer', 'llvm-config', 'llvm-cov', 'llvm-cxxdump', 'llvm-cvtres',
-    'llvm-diff', 'llvm-dis', 'llvm-dwarfdump', 'llvm-exegesis', 'llvm-extract',
-    'llvm-isel-fuzzer', 'llvm-ifs', 'llvm-install-name-tool',
-    'llvm-jitlink', 'llvm-opt-fuzzer', 'llvm-lib',
+    'llvm-addr2line', 'llvm-bcanalyzer', 'llvm-config', 'llvm-cov',
+    'llvm-cxxdump', 'llvm-cvtres', 'llvm-diff', 'llvm-dis', 'llvm-dwarfdump',
+    'llvm-exegesis', 'llvm-extract', 'llvm-isel-fuzzer', 'llvm-ifs',
+    'llvm-install-name-tool', 'llvm-jitlink', 'llvm-opt-fuzzer', 'llvm-lib',
     'llvm-link', 'llvm-lto', 'llvm-lto2', 'llvm-mc', 'llvm-mca',
     'llvm-modextract', 'llvm-nm', 'llvm-objcopy', 'llvm-objdump',
     'llvm-pdbutil', 'llvm-profdata', 'llvm-ranlib', 'llvm-rc', 'llvm-readelf',
diff --git a/llvm/test/tools/llvm-symbolizer/input-base.test b/llvm/test/tools/llvm-symbolizer/input-base.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-symbolizer/input-base.test
@@ -0,0 +1,33 @@
+# llvm-symbolizer infers the number base from the form of the address.
+RUN: llvm-symbolizer -e /dev/null -a 0x1234 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 0X1234 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 4660 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 011064 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 0b1001000110100 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 0B1001000110100 | FileCheck %s
+RUN: llvm-symbolizer -e /dev/null -a 0o11064 | FileCheck %s
+
+# llvm-symbolizer / StringRef::getAsInteger only accepts the 0o prefix in lowercase.
+RUN: llvm-symbolizer -e /dev/null -a 0O1234 | FileCheck %s --check-prefix=INVALID-NOT-OCTAL-UPPER
+
+# llvm-addr2line always requires hexadecimal, but accepts an optional 0x prefix.
+RUN: llvm-addr2line -e /dev/null -a 0x1234 | FileCheck %s
+RUN: llvm-addr2line -e /dev/null -a 0X1234 | FileCheck %s
+RUN: llvm-addr2line -e /dev/null -a 1234 | FileCheck %s
+RUN: llvm-addr2line -e /dev/null -a 01234 | FileCheck %s
+RUN: llvm-addr2line -e /dev/null -a 0b1010 | FileCheck %s --check-prefix=HEXADECIMAL-NOT-BINARY
+RUN: llvm-addr2line -e /dev/null -a 0B1010 | FileCheck %s --check-prefix=HEXADECIMAL-NOT-BINARY
+RUN: llvm-addr2line -e /dev/null -a 0o1234 | FileCheck %s --check-prefix=INVALID-NOT-OCTAL-LOWER
+RUN: llvm-addr2line -e /dev/null -a 0O1234 | FileCheck %s --check-prefix=INVALID-NOT-OCTAL-UPPER
+
+CHECK: 0x1234
+CHECK-NEXT: ??
+
+HEXADECIMAL-NOT-BINARY: 0xb1010
+HEXADECIMAL-NOT-BINARY: ??
+
+INVALID-NOT-OCTAL-LOWER: 0o1234
+INVALID-NOT-OCTAL-LOWER-NOT: ??
+
+INVALID-NOT-OCTAL-UPPER: 0O1234
+INVALID-NOT-OCTAL-UPPER-NOT: ??
diff --git a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp b/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
--- a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
+++ b/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
@@ -181,7 +181,7 @@
   Frame,
 };
 
-static bool parseCommand(StringRef InputString, Command &Cmd,
+static bool parseCommand(bool IsAddr2Line, StringRef InputString, Command &Cmd,
                          std::string &ModuleName, uint64_t &ModuleOffset) {
   const char kDelimiters[] = " \n\r";
   ModuleName = "";
@@ -218,15 +218,21 @@
   // Skip delimiters and parse module offset.
   Pos += strspn(Pos, kDelimiters);
   int OffsetLength = strcspn(Pos, kDelimiters);
-  return !StringRef(Pos, OffsetLength).getAsInteger(0, ModuleOffset);
+  StringRef Offset(Pos, OffsetLength);
+  // GNU addr2line assumes the offset is hexadecimal and allows a redundant
+  // "0x" or "0X" prefix; do the same for compatibility.
+  if (IsAddr2Line)
+    Offset.consume_front("0x") || Offset.consume_front("0X");
+  return !Offset.getAsInteger(IsAddr2Line ? 16 : 0, ModuleOffset);
 }
 
-static void symbolizeInput(StringRef InputString, LLVMSymbolizer &Symbolizer,
-                           DIPrinter &Printer) {
+static void symbolizeInput(bool IsAddr2Line, StringRef InputString,
+                           LLVMSymbolizer &Symbolizer, DIPrinter &Printer) {
   Command Cmd;
   std::string ModuleName;
   uint64_t Offset = 0;
-  if (!parseCommand(StringRef(InputString), Cmd, ModuleName, Offset)) {
+  if (!parseCommand(IsAddr2Line, StringRef(InputString), Cmd, ModuleName,
+                    Offset)) {
     outs() << InputString << "\n";
     return;
   }
@@ -340,12 +346,12 @@
           std::remove_if(StrippedInputString.begin(), StrippedInputString.end(),
                          [](char c) { return c == '\r' || c == '\n'; }),
           StrippedInputString.end());
-      symbolizeInput(StrippedInputString, Symbolizer, Printer);
+      symbolizeInput(IsAddr2Line, StrippedInputString, Symbolizer, Printer);
       outs().flush();
     }
   } else {
     for (StringRef Address : ClInputAddresses)
-      symbolizeInput(Address, Symbolizer, Printer);
+      symbolizeInput(IsAddr2Line, Address, Symbolizer, Printer);
   }
 
   return 0;