diff --git a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
index d95ae4f5278c..ae5cc3091749 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
@@ -234,10 +234,12 @@ SampleProfileMatcher::longestCommonSequence(const AnchorList &AnchorList1,
 void SampleProfileMatcher::matchNonCallsiteLocs(
     const LocToLocMap &MatchedAnchors, const AnchorMap &IRAnchors,
     LocToLocMap &IRToProfileLocationMap) {
-  auto InsertMatching = [&](const LineLocation &From, const LineLocation &To) {
+  auto UpdateMatching = [&](const LineLocation &From, const LineLocation &To) {
     // Skip the unchanged location mapping to save memory.
     if (From != To)
-      IRToProfileLocationMap.insert({From, To});
+      IRToProfileLocationMap.insert_or_assign(From, To);
+    else
+      IRToProfileLocationMap.erase(From);
   };
 
   // Use function's beginning location as the initial anchor.
@@ -250,7 +252,7 @@ void SampleProfileMatcher::matchNonCallsiteLocs(
     auto R = MatchedAnchors.find(Loc);
     if (R != MatchedAnchors.end()) {
       const auto &Candidate = R->second;
-      InsertMatching(Loc, Candidate);
+      UpdateMatching(Loc, Candidate);
       LLVM_DEBUG(dbgs() << "Callsite with callee:" << IR.second.stringRef()
                         << " is matched from " << Loc << " to " << Candidate
                         << "\n");
@@ -258,14 +260,14 @@ void SampleProfileMatcher::matchNonCallsiteLocs(
 
       // Match backwards for non-anchor locations.
       // The locations in LastMatchedNonAnchors have been matched forwards
-      // based on the previous anchor, spilt it evenly and overwrite the
+      // based on the previous anchor, split it evenly and overwrite the
       // second half based on the current anchor.
       for (size_t I = (LastMatchedNonAnchors.size() + 1) / 2;
            I < LastMatchedNonAnchors.size(); I++) {
         const auto &L = LastMatchedNonAnchors[I];
         uint32_t CandidateLineOffset = L.LineOffset + LocationDelta;
         LineLocation Candidate(CandidateLineOffset, L.Discriminator);
-        InsertMatching(L, Candidate);
+        UpdateMatching(L, Candidate);
         LLVM_DEBUG(dbgs() << "Location is rematched backwards from " << L
                           << " to " << Candidate << "\n");
       }
@@ -278,7 +280,7 @@ void SampleProfileMatcher::matchNonCallsiteLocs(
     if (!IsMatchedAnchor) {
       uint32_t CandidateLineOffset = Loc.LineOffset + LocationDelta;
       LineLocation Candidate(CandidateLineOffset, Loc.Discriminator);
-      InsertMatching(Loc, Candidate);
+      UpdateMatching(Loc, Candidate);
       LLVM_DEBUG(dbgs() << "Location is matched from " << Loc << " to "
                         << Candidate << "\n");
       LastMatchedNonAnchors.emplace_back(Loc);
diff --git a/llvm/test/Transforms/SampleProfile/Inputs/pseudo-probe-stale-profile-backward-matching.prof b/llvm/test/Transforms/SampleProfile/Inputs/pseudo-probe-stale-profile-backward-matching.prof
new file mode 100644
index 000000000000..c6f58bea90bb
--- /dev/null
+++ b/llvm/test/Transforms/SampleProfile/Inputs/pseudo-probe-stale-profile-backward-matching.prof
@@ -0,0 +1,6 @@
+test_backward_matching_probe:5000:0
+ 5: 100 foo:100
+ 7: 111
+ 11: 999
+ 12: 400 bar:400
+ !CFGChecksum: 999999
diff --git a/llvm/test/Transforms/SampleProfile/pseudo-probe-stale-profile-backward-matching.ll b/llvm/test/Transforms/SampleProfile/pseudo-probe-stale-profile-backward-matching.ll
new file mode 100644
index 000000000000..56302d959819
--- /dev/null
+++ b/llvm/test/Transforms/SampleProfile/pseudo-probe-stale-profile-backward-matching.ll
@@ -0,0 +1,92 @@
+; REQUIRES: asserts && x86-registered-target
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-backward-matching.prof --salvage-stale-profile -S --debug-only=sample-profile-impl,sample-profile-matcher 2>&1 | FileCheck %s
+
+; Test that backward matching in matchNonCallsiteLocs correctly overwrites
+; forward-matched entries for the second half of non-anchor locations between
+; two matched anchors, using pseudo-probe-based profile.
+;
+; IR probes (ordered by probe ID):
+;   1(block), 2(block), 3(call foo), 4(block), 5(block), 6(call bar), 7(block), 8(block)
+;
+; Profile has foo at probe 5 and bar at probe 12 (checksum mismatch triggers
+; stale profile matching).
+;
+; Anchor matching by LCS:
+;   foo: IR probe 3 -> Profile probe 5 (delta = +2)
+;   bar: IR probe 6 -> Profile probe 12 (delta = +6)
+;
+; Block probes [4, 5] are non-anchors between foo and bar.
+; Split evenly:
+;   First half  [probe 4]: forward  delta=+2 -> maps to profile probe 6 (no samples)
+;   Second half [probe 5]: backward delta=+6 -> maps to profile probe 11 (body sample 999)
+;
+; Without the fix, probe 5 stays at forward value 5+2=7 (body sample 111).
+; With the fix (insert_or_assign), backward overwrites to 5+6=11 (body sample
+; 999).
+
+; Verify anchor and non-anchor matching:
+; CHECK: Callsite with callee:foo is matched from 3 to 5
+; CHECK: Location is matched from 4 to 6
+; CHECK: Location is matched from 5 to 7
+; CHECK: Callsite with callee:bar is matched from 6 to 12
+; CHECK: Location is rematched backwards from 5 to 11
+
+; Verify the sample weight at probe 5 uses backward-matched value (999).
+; Without the fix, this would show 111.
+; CHECK: call void @llvm.pseudoprobe(i64 6355742111584357505, i64 5, i32 0, i64 -1){{.*}}weight: 999
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare i32 @foo(i32)
+declare i32 @bar(i32)
+
+define dso_local i32 @test_backward_matching_probe() #0 !dbg !10 {
+entry:
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 1, i32 0, i64 -1), !dbg !14
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 2, i32 0, i64 -1), !dbg !14
+  ; call foo — probe ID 3 encoded in discriminator 186646559
+  %r1 = call i32 @foo(i32 1), !dbg !15
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 4, i32 0, i64 -1), !dbg !14
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 5, i32 0, i64 -1), !dbg !14
+  ; call bar — probe ID 6 encoded in discriminator 186646583
+  %r2 = call i32 @bar(i32 2), !dbg !17
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 7, i32 0, i64 -1), !dbg !14
+  call void @llvm.pseudoprobe(i64 6355742111584357505, i64 8, i32 0, i64 -1), !dbg !14
+  %sum = add i32 %r1, %r2
+  ret i32 %sum, !dbg !14
+}
+
+declare void @llvm.pseudoprobe(i64, i64, i32, i64) #1
+
+attributes #0 = { nounwind uwtable "use-sample-profile" }
+attributes #1 = { mustprogress nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+!llvm.pseudo_probe_desc = !{!13}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 19.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test_probe_bm.c", directory: "/tmp")
+!2 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!3 = !{i32 7, !"Dwarf Version", i32 5}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 7, !"uwtable", i32 2}
+!7 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!8 = !{!"clang version 19.0.0"}
+!9 = !DIFile(filename: "test_probe_bm.c", directory: "/tmp")
+!10 = distinct !DISubprogram(name: "test_backward_matching_probe", scope: !9, file: !9, line: 10, type: !11, scopeLine: 10, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!11 = !DISubroutineType(types: !12)
+!12 = !{}
+; GUID=6355742111584357505, CFGChecksum=123456 (mismatches profile's 999999)
+!13 = !{i64 6355742111584357505, i64 123456, !"test_backward_matching_probe"}
+; Generic debug location for block probes
+!14 = !DILocation(line: 11, column: 3, scope: !10)
+; call foo — discriminator 186646559 encodes probe ID 3, type=direct call
+!15 = !DILocation(line: 12, column: 8, scope: !16)
+!16 = !DILexicalBlockFile(scope: !10, file: !9, discriminator: 186646559)
+; call bar — discriminator 186646583 encodes probe ID 6, type=direct call
+!17 = !DILocation(line: 14, column: 8, scope: !18)
+!18 = !DILexicalBlockFile(scope: !10, file: !9, discriminator: 186646583)