diff --git a/eo-maven-plugin/src/main/resources/org/eolang/maven/unphi/atoms-with-bound-attrs.xsl b/eo-maven-plugin/src/main/resources/org/eolang/maven/unphi/atoms-with-bound-attrs.xsl
index ac08250520..7de145bc38 100644
--- a/eo-maven-plugin/src/main/resources/org/eolang/maven/unphi/atoms-with-bound-attrs.xsl
+++ b/eo-maven-plugin/src/main/resources/org/eolang/maven/unphi/atoms-with-bound-attrs.xsl
@@ -49,7 +49,14 @@ SOFTWARE.
             </xsl:when>
             <xsl:otherwise>
               <xsl:text>.</xsl:text>
-              <xsl:value-of select="."/>
+              <xsl:choose>
+                <xsl:when test=".='φ'">
+                  <xsl:text>@</xsl:text>
+                </xsl:when>
+                <xsl:otherwise>
+                  <xsl:value-of select="."/>
+                </xsl:otherwise>
+              </xsl:choose>
             </xsl:otherwise>
           </xsl:choose>
         </xsl:for-each>
diff --git a/eo-maven-plugin/src/test/resources/org/eolang/maven/unphi/normalized-atom.yaml b/eo-maven-plugin/src/test/resources/org/eolang/maven/unphi/normalized-atom.yaml
index d7c4c88306..5281809db7 100644
--- a/eo-maven-plugin/src/test/resources/org/eolang/maven/unphi/normalized-atom.yaml
+++ b/eo-maven-plugin/src/test/resources/org/eolang/maven/unphi/normalized-atom.yaml
@@ -21,9 +21,9 @@
 # SOFTWARE.
 ---
 asserts:
-  - //o[@base='org.eolang.io.stdout' and not(@abstract) and @name='x']
-  - //o[@base='org.eolang.io.stdout' and not(@abstract) and @name='x']/o[@as='text' and @base='.bytes']
-  - //o[@base='org.eolang.io.stdout' and not(@abstract) and @name='x']/o[@as='size' and @base='.int']
+  - //o[@base='org.eolang.io.stdout' and @name='x']/o[@as='text' and @base='.bytes']
+  - //o[@base='org.eolang.io.stdout' and @name='x']/o[@as='size' and @base='.int']
+  - //o[@base='org.eolang.malloc.@' and @name='y']/o[@as='arg' and @base='.nan']
 phi: |
   {
     ⟦
@@ -37,6 +37,10 @@ phi: |
               ),
               λ ⤍ Lorg_eolang_io_stdout
             ⟧,
+            y ↦ ⟦
+              arg ↦ Φ.org.eolang.nan,
+              λ ⤍ Lorg_eolang_malloc_φ
+            ⟧,
             λ ⤍ Package
           ⟧,
           λ ⤍ Package
diff --git a/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4 b/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
index b1ff0821e6..e44380e457 100644
--- a/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
+++ b/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
@@ -83,7 +83,7 @@ lambdaBinding
     ;
 
 FUNCTION
-    : [A-Z] ~[ \r\n\t,.|':;!\-?\][}{)(⟧⟦]*
+    : [A-Z][A-Za-z_φ]*
     ;
 
 application