diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -666,7 +666,8 @@
   if (V->getType()->isPointerTy()) {
     if (RetainedKnowledge RK = getKnowledgeValidInContext(
             V, {Attribute::Alignment}, Q.CxtI, Q.DT, Q.AC)) {
-      Known.Zero.setLowBits(Log2_32(RK.ArgValue));
+      if (RK.ArgValue)
+        Known.Zero.setLowBits(Log2_32(RK.ArgValue));
     }
   }
 
diff --git a/llvm/test/Analysis/ValueTracking/pr48713.ll b/llvm/test/Analysis/ValueTracking/pr48713.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/pr48713.ll
@@ -0,0 +1,11 @@
+; RUN: opt -instsimplify < %s
+
+define i8* @PR48713() {
+  %call = call i8* @PR48713()
+  call void @llvm.assume(i1 true) [ "align"(i8* %call, i64 0) ]
+  %cmp = icmp eq i8* %call, null
+  %conv = zext i1 %cmp to i32
+  ret i8* null
+}
+
+declare void @llvm.assume(i1 noundef)