diff --git a/ChangeLog b/ChangeLog
index 537e17186..a39dc226d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2025-11-01 Iñaki Ucar <iucar@fedoraproject.org>
+
+	* inst/include/Rcpp/hash/IndexHash.h: Normalize values for all comparisons
+	* inst/include/Rcpp/hash/SelfHash.h: Idem
+	* inst/tinytest/test_sugar.R: Add test for signed zeroes
+
 2025-10-21 Iñaki Ucar <iucar@fedoraproject.org>
 
 	* inst/include/Rcpp/exceptions_impl.h: use __has_include to simplify checks
diff --git a/inst/include/Rcpp/hash/IndexHash.h b/inst/include/Rcpp/hash/IndexHash.h
index de994cbbc..6bc73ed3d 100644
--- a/inst/include/Rcpp/hash/IndexHash.h
+++ b/inst/include/Rcpp/hash/IndexHash.h
@@ -4,7 +4,8 @@
 //
 // Copyright (C) 2010, 2011   Simon Urbanek
 // Copyright (C) 2012 - 2013  Dirk Eddelbuettel and Romain Francois
-// Copyright (C) 2014 - 2021  Dirk Eddelbuettel, Romain Francois and Kevin Ushey
+// Copyright (C) 2014 - 2024  Dirk Eddelbuettel, Romain Francois and Kevin Ushey
+// Copyright (C) 2025         Dirk Eddelbuettel, Romain Francois, Kevin Ushey and Iñaki Ucar
 //
 // This file is part of Rcpp.
 //
@@ -159,13 +160,15 @@ namespace Rcpp{
         #endif
         }
 
+        STORAGE normalize(STORAGE val) const { return val; }
+
         inline bool not_equal(const STORAGE& lhs, const STORAGE& rhs) {
-            return ! internal::NAEquals<STORAGE>()(lhs, rhs);
+            return ! internal::NAEquals<STORAGE>()(normalize(lhs), rhs);
         }
 
         bool add_value(int i){
             RCPP_DEBUG_2( "%s::add_value(%d)", DEMANGLE(IndexHash), i )
-            STORAGE val = src[i++] ;
+            STORAGE val = normalize(src[i++]);
             uint32_t addr = get_addr(val) ;
             while (data[addr] && not_equal( src[data[addr] - 1], val)) {
               addr++;
@@ -199,6 +202,15 @@ namespace Rcpp{
         uint32_t get_addr(STORAGE value) const ;
     } ;
 
+    template <>
+    inline double IndexHash<REALSXP>::normalize(double val) const {
+        /* double is a bit tricky - we have to normalize 0.0, NA and NaN */
+        if (val == 0.0) val = 0.0;
+        if (internal::Rcpp_IsNA(val)) val = NA_REAL;
+        else if (internal::Rcpp_IsNaN(val)) val = R_NaN;
+        return val;
+    }
+
     template <>
     inline uint32_t IndexHash<INTSXP>::get_addr(int value) const {
         return RCPP_HASH(value) ;
@@ -211,10 +223,6 @@ namespace Rcpp{
           uint32_t u[2];
         };
       union dint_u val_u;
-      /* double is a bit tricky - we nave to normalize 0.0, NA and NaN */
-      if (val == 0.0) val = 0.0;
-      if (internal::Rcpp_IsNA(val)) val = NA_REAL;
-      else if (internal::Rcpp_IsNaN(val)) val = R_NaN;
       val_u.d = val;
       addr = RCPP_HASH(val_u.u[0] + val_u.u[1]);
       return addr ;
diff --git a/inst/include/Rcpp/hash/SelfHash.h b/inst/include/Rcpp/hash/SelfHash.h
index 20607277d..1f566da56 100644
--- a/inst/include/Rcpp/hash/SelfHash.h
+++ b/inst/include/Rcpp/hash/SelfHash.h
@@ -3,8 +3,9 @@
 // hash.h: Rcpp R/C++ interface class library -- hashing utility, inspired
 // from Simon's fastmatch package
 //
-// Copyright (C) 2010, 2011  Simon Urbanek
-// Copyright (C) 2012  Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2010, 2011   Simon Urbanek
+// Copyright (C) 2012 - 2024  Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2025         Dirk Eddelbuettel, Romain Francois and Iñaki Ucar
 //
 // This file is part of Rcpp.
 //
@@ -60,10 +61,16 @@ namespace sugar{
         std::vector<int> indices ;
         int size_ ;
 
+        STORAGE normalize(STORAGE val) const { return val; }
+
+        inline bool not_equal(const STORAGE& lhs, const STORAGE& rhs) {
+            return ! internal::NAEquals<STORAGE>()(normalize(lhs), rhs);
+        }
+
         int add_value_get_index(int i){
-            STORAGE val = src[i++] ;
+            STORAGE val = normalize(src[i++]);
             unsigned int addr = get_addr(val) ;
-            while (data[addr] && src[data[addr] - 1] != val) {
+            while (data[addr] && not_equal( src[data[addr] - 1], val)) {
               addr++;
               if (addr == static_cast<unsigned int>(m)) addr = 0;
             }
@@ -90,6 +97,15 @@ namespace sugar{
         unsigned int get_addr(STORAGE value) const ;
     } ;
 
+    template <>
+    inline double SelfHash<REALSXP>::normalize(double val) const {
+        /* double is a bit tricky - we have to normalize 0.0, NA and NaN */
+        if (val == 0.0) val = 0.0;
+        if (internal::Rcpp_IsNA(val)) val = NA_REAL;
+        else if (internal::Rcpp_IsNaN(val)) val = R_NaN;
+        return val;
+    }
+
     template <>
     inline unsigned int SelfHash<INTSXP>::get_addr(int value) const {
         return RCPP_HASH(value) ;
@@ -102,10 +118,6 @@ namespace sugar{
           unsigned int u[2];
         };
       union dint_u val_u;
-      /* double is a bit tricky - we nave to normalize 0.0, NA and NaN */
-      if (val == 0.0) val = 0.0;
-      if (internal::Rcpp_IsNA(val)) val = NA_REAL;
-      else if (internal::Rcpp_IsNaN(val)) val = R_NaN;
       val_u.d = val;
       addr = RCPP_HASH(val_u.u[0] + val_u.u[1]);
       return addr ;
diff --git a/inst/tinytest/test_sugar.R b/inst/tinytest/test_sugar.R
index c92d09cef..4465cedf7 100644
--- a/inst/tinytest/test_sugar.R
+++ b/inst/tinytest/test_sugar.R
@@ -708,6 +708,8 @@ expect_equal(sort(unique(x)), sort(runit_unique_dbl(x)), info = "unique / numeri
 x <- c(x, NA, NA)
 expect_equal(sort(unique(x), na.last = TRUE), sort(runit_unique_dbl(x), na.last = TRUE), info = "unique / numeric / with NA")
 
+x <- c(x, -0.0, +0.0)
+expect_equal(sort(unique(x)), sort(runit_unique_dbl(x)), info = "unique / numeric / with signed 0s")
 
 #    test.sort_unique <- function() {
 set.seed(123)